Just recently, the wii hackers Brushing and Segher found an game-save exploit for the legand of zelda (very similar to the PSP's GTA save-game exploit) that allows the execution of "unsigned" code. it only allows for four lines of code to be exicuted, but hopefully will result in a homebrew loader.
source:
http://tehskeen.com/
NOTE: the source may change, its the only thing on tehskeen's page now because of heavy traffic