That might be one of the most insane plans ever and I hope you know what you try to do here... Anyway:
- Start by understanding how USB works. You want to choose the port based on what device is plugged in, not based where it is physically located.
- Second step: Design a protocol which is able to route audio and video over USB.
- 3rd step: Implement that protocol (maybe start here: https://github.com/devkitPro/wut/blob/master/include/nsysuhs/uhs.h ).
- 4th step: Design and build hardware (a USB device to connect to the Wii U) which uses that protocol and passes it to HDMI or whatever you want as output.
Note that this doesn't take the fact into account that the Wii Us CPU will be too slow to encode the image in realtime. Not sure if the Wii U has dedicated encoding hardware or decoding only...