[bertan]

Why not replace XCode with brew version entirely:

  sudo cp /Applications/Xcode.app/Contents/Developer/usr/bin/git /somewhere/to/backup/just/in/case
  sudo rm /Applications/Xcode.app/Contents/Developer/usr/bin/git
  sudo ln -s /usr/local/bin/git /Applications/Xcode.app/Contents/Developer/usr/bin/git

[nerdponx]

I wonder what would happen if you did this and then tried to uninstall Xcode

[hoke_t]

or just

   sudo cp /usr/local/bin/git /Applications/Xcode.app/Contents/Developer/usr/bin/git