Stock firmware
0. Update to the official 1.5 firmware first, and set region override to true.
1. Place the "SwissFlasher.gcm" bootable ISO for your region onto the WBFS formatted SD card using WBFS Manager 4.0.
2. Boot this "Swiss" ISO up on your GameCube.
3. This will boot up a custom version of Swiss and it should present you with a directory as seen in the picture below.
4. Enter the directory and select the FZN file (Use PAL only if there are more than just that one present), click on the file and follow the prompts to flash Swiss onto the Wiikey Fusion.
5. Once complete, remember you will need to use a FAT32 formatted SD(HC) card with your wiikey fusion!