Run controls to PC and 360

I'm working on a MAME cabinet and I'd like to throw a 360 in there for SF4. If I use a 360 board for the controls, is it possible to run it to the PC and 360 at the same time so I wouldn't have to unplug/plug-in anything? I was thinking if the PC is off, just wire a button to the Guide button to start the 360 and play from there. If I want to play MAME, turn off the 360 and the PC should pick up the 360 controller and use it properly.

Could I just use a USB splitter or am I way off base here?