Hi soatley,

You can use the RadSplitter's client-side API to reference the DIV element which represents the title of the RadSlidingPane and attach an onclick handler which undocks the pane. I prepared for you a sample script, which you can use as a start point and improve it according to your preferences:

 <form id="form1" runat="server">
        <asp:ScriptManager ID="ScriptManager" runat="server" />

        <script type="text/javascript">

        function OnClientLoaded(sender, args)
        {
           var slidingPane = $find("<%=slide1.ClientID %>");
           var titleElement = slidingPane.getSlidingContainerTitle();
           titleElement.onclick = closePane;
        }
       
        function closePane()
        {
          $find("<%=zone.ClientID%>").undockPane($find("<%=slide1.ClientID %>").get_id());
        }
        </script>

        <telerik:RadSplitter Skin="Office2007" SplitBarsSize="4" ID="RadSplitter1" runat="server"
            Orientation="Horizontal">
            <telerik:RadPane ID="pane1" runat="server" Height="22">
                <telerik:RadSlidingZone ID="zone" runat="server" OnClientLoaded="OnClientLoaded">
                    <telerik:RadSlidingPane ID="slide1" runat="server" Title="First">
                    </telerik:RadSlidingPane>
                </telerik:RadSlidingZone>
            </telerik:RadPane>
            <telerik:RadSplitBar ID="bar1" runat="server" />
            <telerik:RadPane ID="RadPane1" runat="server">
            </telerik:RadPane>
        </telerik:RadSplitter>
    </form>
 

All the best,