This sounds good to me; my `python -m venv venv` commands are also almost always followed up by `venv/bin/python -m pip install -U pip setuptools wheel`.  I wouldn't get the `wheel` from this, but it's not always necessary anyway.

Rather than importing or forking, I would expect this could just be done by invoking the venv's pip as a subprocess.

Also, it would need to be a different flag than `--upgrade`, which already exists.