AJAX popup control extender - how do I put on a Cancel button?

Normally with an AJAX popup control extender, you simply select the item and your selection will populate the associated control. However if I want to populate the control either directly or by a drop down list, then I would like to have a submit button and a cancel button. I have found how to put in a Submit button. But how do I put in a cancel button?

            <asp:TextBox runat="server" ID="txtWeek1MonAMTimeIn" Width="40px" />
            <cc1:PopupControlExtender 
                ID="PopupControlExtenderWeek1TimeIn" runat="server" 
                PopupControlID="pnlWeek1MonAMTimeIn" 
                Position="Bottom" 
                TargetControlID="txtWeek1MonAMTimeIn"
                >
            </cc1:PopupControlExtender>  

<!-- Panel for editing data -->
<asp:UpdatePanel runat="server" ID="UDPWeek1MonAMTimeIn">
    <ContentTemplate>
        <asp:Panel runat="server" ID="pnlWeek1MonAMTimeIn" CssClass="popupControl" 
            onprerender="pnlWeek1MonAMTimeIn_PreRender">
            <div class="span-7" style="padding:10px;">
                <div>
                    <div class="span-2">
                        Time In 
                    </div>
                    <div class="span-5">
                        <lib:input runat="server" id="libWeek1MonAMTimeIn" DataType="Time" />
                    </div>
                </div>
                <div>
                    <div class="span-2">
                        Time Out 
                    </div>
                    <div class="span-5">
                    <lib:input runat="server" id="libWeek1MonAMTimeOut" DataType="Time" />开发者_StackOverflow中文版
                    </div>
                </div>
                <div>
                    <div class="span-2">
                        Not in 
                    </div>
                    <div class="span-5">
                    <asp:DropDownList runat="server" ID="ddlLeaveWeek1MonAM" />
                    </div>
                </div>
                <div>
                    <div class="span-2">
                        <asp:Button runat="server" ID="btnCancelWeek1MonAMTimeIn" UseSubmitBehavior="false" Text="Cancel" onclick="btnCancelWeek1MonAMTimeIn_Click" />
                    </div>
                    <div class="span-5">
                <asp:Button runat="server"  ID="btnSubmitWeek1MonAMTimeIn"  Text="Submit" 
                            UseSubmitBehavior="false" onclick="btnSubmitWeek1MonAMTimeIn_Click"  /></div>
                </div>
            </div>
        </asp:Panel>
    </ContentTemplate>
</asp:UpdatePanel>

protected void btnSubmitWeek1MonAMTimeIn_Click(object sender, EventArgs e)
{
    PopupControlExtender.GetProxyForCurrentPopup(this.Page).Commit(string.Empty);
}

use ModalPopupExtender,

it has CancelControlId as property

http://www.asp.net/AJAX/AjaxControlToolkit/Samples/ModalPopup/ModalPopup.aspx