You don't need to mod it, the Datel SD medial launcher will let your run GCOS, Snes9xGx and other homebrew too:
http://us.codejunkies.com/Products/GameCub...__EF000589.aspx
$19.99 plus the cost of a SD card if you don't laredy have one.
Edit, not 100% sure this works on a wii, I think it does...