Can't install virtualenvwrapper on OSX 10.11 El Capitan
You can manually install the dependencies that don't exist on a stock 10.11 install, then install the other packages with --no-deps to ignore the dependencies. That way it will skip six (and argparse which is also already installed). This works on my 10.11 beta 6 install:
sudo pip install pbr
sudo pip install --no-deps stevedore
sudo pip install --no-deps virtualenvwrapper
And no need to disable rootless.
sudo pip install virtualenvwrapper --ignore-installed six
Also works