A little off-topic, but have you thought of supporting actual controllers for the game? I have some things I screwed around with a few months back to support alternate controllers for my engine, maybe you're interested..
x360 Guitar Controller (USB):
x360 Guitar Controller (USB):
JoyDown(32) = green button JoyDown(1) = red button JoyDown(3) = yellow button JoyDown(2) = blue button JoyDown(4) = orange button JoyDown(6) = back button JoyDown(7) = start button JoyHat(0) = Flipper values JoyU(0) = Whammy values