I can tell you ahead of time that n64 plugins only allow you to remap inputs globally. You can't do it on a per game basis. Why? Because the plugins are intended to be used to remap your controls to a gamepad, preferably a n64 one.
Considering the wcw games need a whopping 9 buttons to be playable you might as well give it up. (a,b, c arrows, L, R, and analog stick tap)
As I said, console games have no business on an arcade panel. Even the other game you mentioned, mario kart, requires an analog stick (or better yet steering wheel) to be played properly. You can play it on digital controls, but it's kinda like playing all those cool-looking racing games on the psp....... akward, and not worth the time/money.