Im not sure if there are cheats for that game. It doesn't seem like the kind of game that would have cheats, but then again Wii Sports did. There isn't any I know of.
appearently there are two; if you press the 1+2 buttons when starting the paddlegame, the paddles should change somehow. I can't get it to work though..but it's not really an exciting cheat anyways.. dont remember the other one..,.