Virtualenv specific pip config files
Found this after I had posted the question:
https://pip.pypa.io/en/stable/user_guide/#config-file
~/.pip/pip.conf
You will need to set:
~/.virtualenvs/env1/pip.conf
~/.virtualenvs/env2/pip.conf
It will still inherit from:
~/.pip/pip.conf
But will allow it to be overwritten for each environment.
Just to update the answer here with the latest from the pip documentation:
Inside a virtualenv:
On Unix and macOS the file is $VIRTUAL_ENV/pip.conf
On Windows the file is: %VIRTUAL_ENV%\pip.ini
The $VIRTUAL_ENV environment variable gets set once you've activated the particular virtual environment you're interested in.