For all courses, boards, and 1 extra boarder:
D= Digital Stick
A= Analog Stick
C= Yellow Buttons

At the Main Menu, press:

Ddown, Dup, Adown, Aup, Cdown, Cup, L, R, Z, Aleft, Cright, Dup, B, Aright, Cleft, Start

You know it works when you hear a "Yeah!" after pressing Start...