FretFury is a homebrew in the making that utilizes the Guitar Grip that comes with Guitar Hero: On Tour for the Nintendo DS. If you don't have the Guitar Grip, there is a version where you use the Y,X,B,A buttons!
I don't have a wii u anymore to test it myself, but if homebrews are not visible on the wii u menu I think you can press L + R + minus to open the plugin menu, there should be an option called "homebrews on wii u menu" or something similar