Clarification: Many games offer an Off-TV Play mode where the Gamepad gets the main content rather than map, inventory &c., so you don't need access to the TV. There is a homebrew program (SwapDRC) that will force this on any Wii U game.
If you really want to connect the Wii U to another TV without doing the easy thing, as Urbanshadow points out, of actually moving the console, you can get HDMI transmitters & receivers. But these would be connected to the HDMI port on the back of the console, not added to the Gamepad.