Button inputs work
While it's been operating on a few other platforms for a while now, the online portal PlayBoxie is now compatible with Nintendo's Wii U. Basically all you do is visit PlayBoxie on an Xbox One, PS4, Wii U, or PC, and you're good to go. Button inputs will work just like a normal game.
Don't get too excited -- the selection isn't that great, and the framerates leave much to be desired. But it's still something extra to do on your Wii U while you wait for Donkey Kong Country Returns: Tropical Freeze to drop.