This tells you how to download a wheel, but how do you actually use it? There's also this, but I don't want that, I just want to build my own version that supports older glibcs (because AL2 is a thing). I looked at the docs for scie-pants, since the restricted Internet bit mentions that, and I think that's the way to go, but that only mentions URLs, can you use files?

Yeah, a

file://

URL allows pointing to a local file