Using the WiiKey Fusion
To load a game from SD card boot the Wii console with no disc in the console and a SD card in the WiiKey Fusion external SD card reader.
When the main menu loads a GameCube game will show in the disc channel.
Press start and the WiiKey menu will be loaded.
The menu is controlled using the reset button on the front of the Wii, a brief press cycles to the next item in the list, holding the reset button on an item will open/load the item.
To load a game cycle through the items till you get to the one you want, i.e. in the image above to load Wii Music, the reset button should be pressed 2 times then the reset button held. Once you have held the reset button to load the item you would like, the Wii will reset, the game/item you selected will now show in the disc channel, simply select and play.
When you want to change the game, at the Wii main menu press eject then reset the console, when the Wii main menu re-appears, the WiiKey menu (GameCube Icon) will show back in the disc channel allowing you to choose your next game. Simple as that!