I was wondering about this when I decided I wanted to make use of my SD Gecko I had from my gamecube, as I no longer use my gamecube for homebrew anymore. In essence I thought the Homebrew Channel made use of almost all the homebrew loading methods, and therefore could make use of two of my SD cards at once, though apparantly not from a SD Gecko. I also just had the idea that Save Game Manager may be able to utilize such a modification in that it can installs saves that are on the Wiis memory, and since the Wii can see saves from a GC memory card that maybe it would be possible that it could also allow installing GC saves back onto a GC memory card. That would be accomplished by the GC memory card being in a respective memory card slot, from which the Wii would see the saves and therefore they would exist on the Wii so long as the card remained plugged in.
Anyways it's just an idea, and I myself have no idea how to accomplish this, but we all know the Wii doesnt need to be in GC mode to see the GC memory cards so perhaps this area could be enhanced upon for those who primarily use SD cards for their homebrew needs. Thanks for reading and giving input into this.