For the time being the function can be set through the kendoWidget:

<telerik:RadHtmlChart runat="server" ID="ColumnChart1" Transitions="true">
    <PlotArea>
        <Series>
            <telerik:ColumnSeries Name="Product 1">
                <TooltipsAppearance BackgroundColor="Orange" DataFormatString="{0} sales" />
                <SeriesItems>
                    <telerik:CategorySeriesItem Y="15000" />
                    <telerik:CategorySeriesItem Y="23000" />
                    <telerik:CategorySeriesItem Y="10000" />
                    <telerik:CategorySeriesItem Y="16000" />
                </SeriesItems>
            </telerik:ColumnSeries>
        </Series>
        <XAxis AxisCrossingValue="0" Color="Black" MajorTickType="Outside" MinorTickType="Outside"
            Reversed="false">
            <Items>
                <telerik:AxisItem LabelText="1" />
                <telerik:AxisItem LabelText="2" />
                <telerik:AxisItem LabelText="3" />
                <telerik:AxisItem LabelText="4" />
            </Items>
            <LabelsAppearance DataFormatString="Q{0}" RotationAngle="0" />
            <MajorGridLines Color="#EFEFEF" Width="1" />
            <MinorGridLines Color="#F7F7F7" Width="1" />
            <TitleAppearance Position="Center" RotationAngle="0" Text="Quarters" />
        </XAxis>
        <YAxis AxisCrossingValue="0" Color="Black" MajorTickSize="1" MajorTickType="Outside"
            MaxValue="50000" MinorTickSize="1" MinorTickType="Outside" MinValue="0" Reversed="false"
            Step="10000">
            <LabelsAppearance DataFormatString="{0} sales" RotationAngle="0" />
            <TitleAppearance Position="Center" RotationAngle="0" Text="Sales" />
        </YAxis>
    </PlotArea>
    <ChartTitle Text="Product Sales for 2011">
    </ChartTitle>
    <Legend>
        <Appearance Position="Bottom" />
    </Legend>
</telerik:RadHtmlChart>
<script>
    function pageLoad() {
        $ = $telerik.$;
        var kendoWidget = $find("<%=ColumnChart1.ClientID%>").get_kendoWidget();
        kendoWidget.options.series[0].labels.position = function (point) {
            if (point.value < 20000) {
                console.log(1);
                return "insideEnd";
            } else {
                console.log(2);
                return "outsideEnd";
            }
        }
        kendoWidget.redraw();
    }
</script>