pip install --download -> pip download
pip install --no-install -> pip unpack
pip install --no-download -> get rid of it (see comments from @g2p below)

along with this, move to mkdtemp build dirs (instead of static ones) in virtualenvs and global installs.
I think the --no-install/--no-download "workflow" is what fueled the static build dirs pip has, which have caused so many problems.