What's the easiest way to get a GWT PopupPanel to show in front of Google Earth Plugin

Question

I am using the GWT MapWidget to view Google Earth but it seems that PopupPanels are being shown behind the earth view in Firefox. It works correctly when other map types like satellite and in IE. I understand that the way to get this to work is to use an IFrame shim but I'm not sure how to do this easily in GWT. Apparently, PopupImplIE6 already uses this technique but not the one used in Firefox.