The lines can be similar to the ones in the box plot chart type - http://www.telerik.com/help/aspnet-ajax/htmlchart-types-box-plot-chart.html .

For the time being you can use transparent box plot series in order to simulate this. For example:

ASPX:

        <telerik:RadScriptManager ID="RadScriptManager1" runat="server"></telerik:RadScriptManager>
		<script>
			function pageLoad() {
				//Attach the legendItemClick event on pageLoad:
				var chart = $find("<%=RadHtmlChart1.ClientID%>")._chartObject.bind("legendItemClick", OnLegendClicked);
			}
			function OnLegendClicked(e) {
				if (e.seriesIndex >= 3) {
					var meanSeriesVisible = e.sender.options.series[3].visible;
					var medianSeriesVisible = e.sender.options.series[4].visible;

					if (meanSeriesVisible == medianSeriesVisible) {
						if (e.series.visible == false) {
							e.sender.options.series[5].visible = false;
						}
					}
					else {
						if (e.series.visible == false) {
							e.preventDefault();
							e.sender.options.series[3].visible = false;
							e.sender.options.series[4].visible = false;
							e.sender.options.series[5].visible = true;
							e.sender.options.transitions = false;
							e.sender.redraw();
						}
					}
				}
			}
		</script>
        <telerik:RadHtmlChart runat="server" ID="RadHtmlChart1" Width="1000" Height="500">
            <PlotArea>
                <Series>
                    <telerik:ColumnSeries Name="Germany Gold" GroupName="Germany" Gap="1">
                        <Appearance>
                            <FillStyle BackgroundColor="#DDD9C3" />
                        </Appearance>
                        <SeriesItems>
                            <telerik:CategorySeriesItem Y="13" />
                            <telerik:CategorySeriesItem Y="12" />
                            <telerik:CategorySeriesItem Y="16" />
                        </SeriesItems>
                        <TooltipsAppearance ClientTemplate="#= series.name# medals: #= dataItem.value#" />
                        <LabelsAppearance Visible="false"></LabelsAppearance>
                    </telerik:ColumnSeries>
                    <telerik:ColumnSeries Name="Germany Silver" GroupName="Germany">
                        <Appearance>
                            <FillStyle BackgroundColor="#C4BD97" />
                        </Appearance>
                        <SeriesItems>
                            <telerik:CategorySeriesItem Y="17" />
                            <telerik:CategorySeriesItem Y="16" />
                            <telerik:CategorySeriesItem Y="10" />
                        </SeriesItems>
                        <TooltipsAppearance ClientTemplate="#= series.name# medals: #= dataItem.value#" />
                        <LabelsAppearance Visible="false"></LabelsAppearance>
                    </telerik:ColumnSeries>
                    <telerik:ColumnSeries Name="Germany Bronze" GroupName="Germany">
                        <Appearance>
                            <FillStyle BackgroundColor="#948A54" />
                        </Appearance>
                        <SeriesItems>
                            <telerik:CategorySeriesItem Y="26" />
                            <telerik:CategorySeriesItem Y="20" />
                            <telerik:CategorySeriesItem Y="15" />
                        </SeriesItems>
                        <TooltipsAppearance ClientTemplate="#= series.name# medals: #= dataItem.value#" Color="White" />
                        <LabelsAppearance Visible="false"></LabelsAppearance>
                    </telerik:ColumnSeries>
                    <telerik:BoxPlotSeries Name="Mean" Visible="true">
                        <Appearance>
                            <FillStyle BackgroundColor="Transparent" />
                        </Appearance>
                        <SeriesItems>
                            <telerik:BoxPlotSeriesItem Mean="11" Median="0" Lower="0" Upper="0" Q1="0" Q3="0"></telerik:BoxPlotSeriesItem>
                            <telerik:BoxPlotSeriesItem Mean="15" Median="0" Lower="0" Upper="0" Q1="0" Q3="0"></telerik:BoxPlotSeriesItem>
                            <telerik:BoxPlotSeriesItem Mean="14" Median="0" Lower="0" Upper="0" Q1="0" Q3="0"></telerik:BoxPlotSeriesItem>
                        </SeriesItems>
                    </telerik:BoxPlotSeries>
                    <telerik:BoxPlotSeries Name="Median" Visible="false">
                        <Appearance>
                            <FillStyle BackgroundColor="Transparent" />
                        </Appearance>
                        <SeriesItems>
                            <telerik:BoxPlotSeriesItem Mean="0" Median="12" Lower="0" Upper="0" Q1="0" Q3="0"></telerik:BoxPlotSeriesItem>
                            <telerik:BoxPlotSeriesItem Mean="0" Median="10" Lower="0" Upper="0" Q1="0" Q3="0"></telerik:BoxPlotSeriesItem>
                            <telerik:BoxPlotSeriesItem Mean="0" Median="13" Lower="0" Upper="0" Q1="0" Q3="0"></telerik:BoxPlotSeriesItem>
                        </SeriesItems>
                    </telerik:BoxPlotSeries>
                    <telerik:BoxPlotSeries Name="Mean and Median" Visible="false">
                        <Appearance>
                            <FillStyle BackgroundColor="Transparent" />
                        </Appearance>
                        <SeriesItems>
                            <telerik:BoxPlotSeriesItem Mean="11" Median="12" Lower="0" Upper="0" Q1="0" Q3="0"></telerik:BoxPlotSeriesItem>
                            <telerik:BoxPlotSeriesItem Mean="15" Median="10" Lower="0" Upper="0" Q1="0" Q3="0"></telerik:BoxPlotSeriesItem>
                            <telerik:BoxPlotSeriesItem Mean="14" Median="13" Lower="0" Upper="0" Q1="0" Q3="0"></telerik:BoxPlotSeriesItem>
                        </SeriesItems>
                    </telerik:BoxPlotSeries>
                </Series>
                <YAxis>
                    <TitleAppearance Text="Number of Medals" />
                </YAxis>
                <XAxis>
                    <LabelsAppearance DataFormatString="Year {0}" />
                    <Items>
                        <telerik:AxisItem LabelText="2000" />
                        <telerik:AxisItem LabelText="2004" />
                        <telerik:AxisItem LabelText="2008" />
                    </Items>
                </XAxis>
            </PlotArea>
            <ChartTitle Text="Olympic Medals Per Country Over the Years">
            </ChartTitle>
            <Legend>
                <Appearance Position="Right" />
            </Legend>
        </telerik:RadHtmlChart>