Hi there,
Good idea. I'm not sure if it has been covered specifically by the wii, and especially from the surf point of view. Check out the different types of balance boards you can get and i mean the skate board type ones, there are different types to be found
Tallington Lakes Pro Shop: SCRUB
and you could alter or vary the design to suit surfing theme, maybe along the
lines of a skim board?
Can you imagine using the nun chucks aswell to adapt as a windsurfing or Kite surf game, a bit overcomplicated im sure but well crazy