To make it simple, no, it's not really doable. The real issue here is that the communication protocol would have to be emulated by software and since linux is not a real time OS (at least the standard builds used on raspberries) you can't emulate it properly and keeping the signal timing right.
There's obviously the simple solution of using any kind of GameCube to USB controller converter and use that, but I don't see why anyone should do this
You could always just use the digital pins as digital buttons and hook up an adc for analog. Then just use one of those pi emulator things to use the inputs
You could always just use the digital pins as digital buttons and hook up an adc for analog. Then just use one of those pi emulator things to use the inputs