Why didn't anyone do this sooner? I think the A and B buttons on the DS are difficult to use for GBA games so I installed a switch on the bottom of my DS that lets me use the X button as the B button in GBA games. Download the video to check it out.
On the outside:
Switch
Screen
On the inside -thanks LIK-SANG:
Inside
You need divx codecs for the videos.
Divx
Button Mod
Button Mod 2