The downside on this is that you have to use a computer(these devil machines!)
It needs some skills for soldering and I would have tried it but I don't have any sp for the moment...(this is the part where you make me a present!)
The concept is simple:
Get a usb-joystick(they are really cheap),break it,change the wiring of the buttons to the pads,download a freeware midi utility for using the joystick as notes and you have a nice diy controller...so
Don't throw away your broken sp's
PS.I want 50% of the modders profit....