You're going to want to either set up haxchi with mocha CFW or Coldboot Haxchi (CBHC) but to initially set it up you need an internet connection to run the browser exploit once. Once thats done you won't need a connection anymore. I suggest taking a look at this thread: https://gbatemp.net/threads/guide-community-noob-guide-to-wii-u-hacking.451297/
Also CBHC is risky and can cause a brick if you arent careful. Haxchi by itself is safer. CBHC is more convenient however
the only thing I can think of that might work is BluUbomb. I think that can enter the homebrew launcher without the browser, but I've never tried it. it's an exploit of bluetooth, hence the name.