My plan(when my current joystick dies) is to get one of those usb sticks and rewire it. All that is needed is to bypass the electronics and add a 9pin female dsub. Would probably require a new cable as amiga/c64 joysticks use 6 wires and usb only use 4(or was it 5).
@Amigakit: Maybe you should start selling "rewiring kits" for the "comp pro". 9pin female dsubs dosn't grow on trees these days.