How about installing a light inside of your GBA? Some folks have a little experiment underway...
The kids over at Portable Monopoly.com are rigging a light inside of their GBA to rid the "no backlight" problem.
It's a very interesting project, and if it ends up working, there might be a better lighting solution than what's currently available. Not that I would recommend gutting your GBA! Click here for the juice. Thanks to EAGB for the hook.