That's the first I ever heard of it, either, and was unable to find out if those options are exposed more generally to the CI pipeline (so can I make my own "-o" toys?)

I don't recall ever hearing of any such thing in GitHub, and their help search is so atrocious I don't know that I'd be able to find the answer even now. That said, I can't imagine that kind of customization fits into GitHub's mental model, which goes double given that they just recently even _developed_ a CI system to which one could send those options