Java SE (Java Platform, Standard Edition)

Hi, I'm currently working on a small lib that's meant for displaying, aranging, animating custom user notification popups (like the "new email popup" from Thunderbird in Windows for example).
Of course I'd like to display the popups in respect to the size and position of the taskbar.
I'm using the Toolkit#getScreenInsets Method to calculate the correct place for the popups and it works fine with Windows, but not at all with my Linux system.
The Insets are always 0,0,0,0.
So far I've tried Gnome/Metacity and Beryl.
I've also found some (closed) bugs on that issue but there was no workaround mentioned.
It looks as if it's not really possible to do what I'm planning to do with Gnome.
How about other Window Managers?
Maybe there is a dirty trick that I could use to make it work?

Thanks in advance for any idea.