window on aqua without a titlebar

Tcl/Tk,

I am trying to create a top-level window that does NOT have a titlebar.

I have the following code:

     $img_hover{win} = $mw->new_toplevel();
     $img_hover{win}->g_wm_title ( "Balloon Card Image" );
     $img_hover{win}->g_wm_iconbitmap ( $CONSTANTS{APP_ICON} );
$img_hover{win}->g_wm_geometry("$PM_CONSTANTS{BALLOON_IMG_X}x$PM_CONSTANTS{BALLOON_IMG_Y}"); 

     $img_hover{win}->g_wm_resizable(0, 0); # make window size fixed, 
not resizable
     $img_hover{win}->g_wm_overrideredirect ( 1 );

on Win32, it works fine
on aqua, the window always has a titlebar

In addition, I'm using the window as a tooltip/balloon hover window, so 
when it's shown, I never want it to have the "focus".  When I deiconfy 
it on Win32, it works great, but on OS X (aqua), it shows the window and 
also grabs the focus, so I have to click on the main app to return focus.

Any insight is appreciated.

Thanks,
Mike

ps, I believe I'm using Tcl 8.5.8