Re: 'a bare minimum would be forking'
"Merging is difficuuuuuuult"
no, it's not. do a snapshot and merge to the master branch (on the original) with a pull request from time to time. Easy.
Or you can fork the repo, fix things on your end, and THEN do a pull request into the original repo [which I did a while back with the Arduino project, as an example]. It's the best way to contribute. It's all well documented on github.