That's one way to solve the drought of Wii U games, I suppose. Nintendo wouldn't approve, mind you.
Engadget reports on a hack first shown at the Chaos Communication Congress that runs through reverse engineering the communications between the Wii U Gamepad and its host controller, although this particular hack doesn't appear to need the Wii U itself to work.
It's still early days, so "playing" is essentially just "streaming". It's also nothing that Nintendo will ever support in any way at all, although it is cute that one of the titles demonstrated was an emulator showing the Gamecube version of Wind Waker.