I discovered a few days ago it is possible to bypass the region lock on the Wii U's gamepad. Searching for about an hour turned up "it's impossible" or "wait until someone figures out how to hack the gamepad's firmware." I guess nobody noticed? Figured it was worth sharing here so that anybody else trying to do this doesn't run into a wall.
Quoting myself from the Retro Game Boards Wii U Appreciation and Collecting Thread cause I can't post links apparently.
That's all you need to do. I have a JP region gamepad synced and working with my US region Wii U, but there's no reason to think it won't work for any region gamepad with any region Wii U.
Quoting myself from the Retro Game Boards Wii U Appreciation and Collecting Thread cause I can't post links apparently.
If you try to sync it the proper way, using the button on the system, it’ll sync but you’ll get an error about the Wii U Gamepad needing an update. Dead end.
But, if you have a hacked Wii U, you can install “System Config Tool,” an app intended for debug Wii Us. In there you can break a lot of things on your Wii U so be careful but under “Wii U GamePad (DRC) Settings” you can sync gamepads. Doesn’t seem like it’d be very useful but if you sync an out of region gamepad in here, you won’t get prompted about a gamepad update and can bypass the region lock entirely.
That's all you need to do. I have a JP region gamepad synced and working with my US region Wii U, but there's no reason to think it won't work for any region gamepad with any region Wii U.