Showing JDialog as Sheet

I am currently using this code to create a JDialog;

http://pastebin.com/PJ8VGdPb

I was previously using Java 6 to compile the application and setting the clientProperty

apple.awt.documentModalSheet

was working perfectly to display the dialog as a "Sheet" on OSX but now I started using Java 7 (update 25) and the dialog is no longer displayed as a Sheet. I can't seem to find any update documentation on this. Have they changed anything about this? How can I solve this? The current interface design looks tons better with a Sheet than a dialog.

Update

I found the following Bug report which seems to be the same issue as I am experiencing;

http://bugs.sun.com/view_bug.do?bug_id=8010197

Does anyone know how to resolve this? I have looked into libraries like QuaQua but I would prefer not using any library because I just want the Sheet functionality.

Update 2

I tried QuaQua, but the library currently has the exact same problem when compiling with Java 7. Any workarounds?