Modal PopUp in separate iFrame

I have two iFrames in my web application. The first is a header that contains some buttons, the second is the main content window.

I am trying to click a button in iFrame1 and open a ModalPanel in iFrame2. I imagine others have run into this before. I realize iFrames are not always the best way to go, but I have a music player in my top frame, and I want to keep it playing while users navigate the site.

I'm basically looking for some type of Target attribute to reference iFrame2 as the target, but I'm not having any luck. I found a few hits regarding jQuery, but I have not learned jQuery yet, so I'm stuck with JavaScript, HTML & C# until then.

This is the button I'm using to open the model window in my header frame (iFrame1).

<asp:ImageButton ID="plyrFilter" runat="server" ImageUrl="images/plyrFilter.gif" onmouseover="plyrToolTip('Filter Genre')" onmouseout="plyrToolTip('')" />

This is the model in my header frame (iFrame1).

<!-- Popup Window for filter -->
        <asp:Panel ID="ModalPanel" runat="server" Width="300px">
        <div class="modalPopupWrapper">
            <div class="divCloseBtn"><asp:ImageButton ID="OKButton" runat="server" ImageUrl="~/images/modalClose.png" /></div>
            </div>

            <div class="divContent">
            This is some text. Put the filters in here.

             <asp:Button ID="btnLobtnFilter" runat="server" Text="Apply Filter" />

             </div>
        </asp:Panel>
        <ajaxToolkit:ModalPopupExtender ID="mpe" runat="server"  TargetControlId="plyrFilter" BackgroundCssClass="modalBackground"
        PopupControlID="ModalPanel" OkControlID="OKButton" />
    <!-- Popup Window for filter end -->

Of course this just opens the model window in the header iFrame. How can I get this to open in the main content iFrame (iFrame2)?

Tags: C#, Ajax, ASP.NET, IFrame