I doubt you can. AFAIK, the 360 controller does not have any button configurator thing yet, so the game has to natively support the controller. Then again, you could go sniffing around for some special drivers.
For FF, I would recommend the Logitech Dual Action pad (think that's what it's called). It looks exactly like a PS2 controller, and has its own button config thing. $20 wired, $30 wireless. Check it out at Target.