I prefer a nondestructive approach. I set up an ATTINY85 clone to serve as a DIY USB adapter. Just solder a controller extension cable to the microcontroller to donate the right port, and you have everything you need. You have enough GPIO pins and the requisite 5v logic to make it a great fit. Mine was made for NES controllers, but it uses the same shift logic as the SNES controller, just with fewer buttons.