If you load a game off one memory card, then save it on another one which already has SSBM game data, then again straight away on the first one, both memory cards should have all the characters, trophies and whatnot that the first one had. Simple. Oh, and Giga Bowser's a piece of pie. Even on Very Hard.
10000 posts at last! w00t! Okay, I'm off into a quiet retirement. Don't bother me.