To do that, you will need to install the d2x IOS.
The Definitive Guide mentioned above recommends USB Loader GX (in conjunction with Nintendon't for GameCube Games.)
Just a note that the Wii U will attempt to format your drive if you connect it to the console while in Wii U mode. A tool called UStealth hides it from the Wii U, but not from compatible vWii software, such as USB Loader GX.
If you need any help with vWii, most answers will likely be in that definitive guide, but don't be afraid to ask (as long as you ask valid questions, and don't troll).