Multiple buttons associated with a single ModalPopupExtender

Hi,

Is it possible to have many buttons associated with a single ModalPopupExtender?

<asp:Button ID="btnPopup" runat="server" Text="PopUp" style = "display:none" /> // default control

<asp:Button ID="Button1" runat="server" CssClass="btn btn-primary" 
                            Height="200px" Width="200px" onclick="Button1_Click" /><asp:Button ID="Button2" runat="server" CssClass="btn btn-primary" 
                            Height="200px" Width="200px" onclick="Button2_Click" />

<asp:ModalPopupExtender ID="mpe" runat="server" BackgroundCssClass="modalBackground" PopupControlID="pnlPopup" TargetControlID="btnPopup" /><asp:Panel ID="pnlPopup" runat="server" CssClass="modalPopup" Style="display: none">

        // I will have updatepanel where content will change based on which button is clicked

        </asp:Panel>

protected void Button1_Click(object sender, EventArgs e)
{
     mpe.TargetControlID = "Button1";
}

protected void Button2_Click(object sender, EventArgs e)
{
     mpe.TargetControlID = "Button2";
}

This doesn't seem to work.

Thank you!