A forum goer over at the Max Console forums figured out a neat little trick that allows a PAL Wii to play import GameCube games. It requires a bit of "pebble-snatching-speed" on the part of the young grasshopper (that's you), as upon inserting a PAL GameCube game and going to the Wii's disc channel, seeing the GameCube logo come up, you'll need to have your pointer over the start button. Once you do that, you'll have to eject the GameCube disc and quickly swap it out for your import game, immediately pressing the start button. This'll trick the Wii into thinking the import GameCube game is a PAL title, starting it up and allowing you to play it as normal.
We'd love to give this a try ourselves to confirm that the trick works on NTSC units (we're pretty sure it would anyway), but lack any import GameCube titles to try it on. Instead, we'll pose the challenge to our readers with NTSC consoles and ask them to give it a whirl. Let us know, won't you?