As of right now there is no public exploit for the Wii U side, so no it is not possible to back up Wii U games yet. As soon as there is, it will be posted on this forum.
You can already play old Wii games on the gamepad. This feature was implemented by N themselves through one of the most recent updates. Just start Wii mode and it will prompt you as to if you want to use the gamepad.