You can install a Homebrew formula directly from a pull request by using brew install $raw_pull_requst_url, eg:
brew install https://raw.github.com/ColinHebert/homebrew/538a99cc06a8f40b6ebcf2f4f8fd44d563c672cd/Library/Formula/emacs.rb
For finding the pull request URL, there’s probably a better way, but I went to the pull request URL you linked, clicked on Files Changed, then on View File @ 9b22d42, then finally on Raw