Hm... why wouldn't one of the bumpers on the 360 controller work as a Z stand-in? I could always configure Z to one of the Shoulder or Face buttons (in SSBB's custom controls), but I just don't understand why it wouldn't work.
Wouldn't it carry the "Right Bumper" signal as a "white/black button"(XBOX) signal, to the PS2 Controller as a "R1 Trigger", and then carry THAT to the GC port as a "Z trigger"?







