With project.toml, the new strat is to build the wheel with `python3 -m build` and then install it with `pip install --root=$DESTDIR` plus a handful of flags to tell pip not to touch the network or the local cache.
It's not great, but it's also not terrible.
E.g. https://github.com/cbarrick/efiboot/blob/2ca46a7c27c837adf23...