For the time being you can set the property through the kendoWidget. All available options are available at http://docs.telerik.com/kendo-ui/api/javascript/dataviz/ui/chart#configuration-series.connectors
        <script>
            function pageLoad() {
                var kendoWidget = $find("<%=RadHtmlChart1.ClientID%>")._chartObject;
                kendoWidget.options.series[0].connectors = {width: "3", color: "#ff0000"};
                kendoWidget.redraw();
            }
        </script>
        <telerik:RadHtmlChart ID="RadHtmlChart1" runat="server" Width="400px" Height="400px">
            <PlotArea>
                <Series>
                    <telerik:PieSeries>
                        <SeriesItems>
                            <telerik:PieSeriesItem Y="30" />
                            <telerik:PieSeriesItem Y="10" />
                            <telerik:PieSeriesItem Y="20" />
                        </SeriesItems>
                    </telerik:PieSeries>
                </Series>
            </PlotArea>
        </telerik:RadHtmlChart>