I don't know if the thread creator is still here after so much denial, anyways I'll explain (at least what I was told):
When the Wii enters GC Mode, it disables everything "not-Gamecube" on the console, leaving only the console (of course), the controller ports and the memory card slots on; that means there's no Wiimote compatibility, SD Card support and, of course, USB support. So, it's useless to run Gamecube games on USB, since it will be turned off as soon as the Wii enters Gamecube mode.
Having said that, unless someone finds out how to play GC games without disabling the features of Wii mode, or playing them on Wii mode itself, there's no way I can think of to store and play GC games via USB.
That's a bummer, since people with problems with the Wii disc drive (*COUGHCOUGHCOUGHMECOUGH*) will not be able to play Gamecube through another method, but hopefully, one day somebody will come up with a solution. =)