brew pip allows you to install any pip package as a homebrew formula.
brew install brew-pip
brew pip Mercurial
After you install some pip packages, you will need to add Homebrew's pip path to your PYTHONPATH.
You can add something like the following to your ~/.bash_profile:
export PYTHONPATH=$(brew --prefix)/lib/python2.7/site-packages
brew-pip's half brother brew-gem.