In theory you might be able to unbrick it with:
- An OTP dump from your console
- An OTP dump from another console
- A NAND dump from the same other console
- A hardmod on your console
Basically, you decrypt the other person’s NAND dump, re-encrypt it with your OTP and flash it back to your own Wii U. You should then be able to start afresh from there. If your friends don’t have a Wii U then you could probably build a decrypted NAND dump from system files downloaded through NUSDownloader. Not sure if it will work but its the general way of going about things with a bricked console.
EDIT: I don’t know exactly how to do it, as I’ve never bricked a single system in my life, and always made a NAND dump. But you probably have to invest in some expensive hardware like audrino or progskeet. And it requires some really skilled soldering.