I have been looking for something like this project for a very long time! Being a guitar player, it is difficult for me to control an audio playback interface, with complex multi-key strokes and mouse clicks, while playing guitar with my hands. Taking some ideas from the MAME/X MAME crowd, I recently began hacking at keyboards into a foot controller design. The biggest obstacle is the interface. Now that I have found mp3blaster, I can now design the keyboard-hack-foot controller to control mp3blaster.
Finally, I have all the pieces for my foot controlled mp3 player!
Thank you for creating just the project I am looking for!