The discovery requires some quick finger work.
MaxConsole forum member, dolqube, discovered a method for booting GameCube games from other regions on Wii without resorting to boot discs or modchips. The trick allows booting of any NTSC game on any NTSC system (Japanese games on US systems and vice-versa) as well as booting NTSC games on PAL systems. PAL games on NTSC systems will not work. As of now, the trick appears to work on all firmware versions.
The procedure requires some hand acrobatics, though Wii owners should be used to that kind of thing. It may take a few tries to get the timing down correctly. The method is performed as follows:
1. Insert a GameCube disc from the same region as the Wii into the system and open the Disc Channel.
2. Push the Eject button on the Wii console.
3. Click the Start button on the screen just before it would be deactivated due to taking the disc out. It may help to position the cursor on screen before pressing Eject.
4. Quickly and smoothly remove the ejected disc and insert the import GameCube disc. This must be done before the blue light comes on. If the Wii does not automatically feed the disc, the timing wasn't correct and another attempt will have to be made. Do not try to force the disc in. The system will automatically reboot in this case. Otherwise, the import will boot up!
The procedure works just as well as the Freeloader/Action Replay method of booting discs. This means that Japanese text may not be displayed properly and a select few games will not have save capability. For the most part, however, import games work very well. This method is of course not approved by Nintendo.
