I keep coming back to this thread and this is the first post at the top of the page. I cringe... and then laugh my ass off! Poor Susie! But I bet she kicks ass on a bike now!
My memory is something along the lines of Right-Left-Down-Up-A-B-Select-Start. Heck, it probably doesn't even matter. I bet there are a whole bunch of cheat codes.
I think Ron is right, but I am pretty sure it still worked with select even if it was one player. It just didn't do anything extra. I feel like I always did select-start.