Git hook for merge conflicts

As suggested by Charles Bailey, the best way to do this is by customizing the mergetool. Using this guide, I came up with this simple way to have merge conflicts opened in my editor:

[merge]
  tool = emacs
[mergetool "emacs"]
  cmd = $editor \"$BASE\" \"$LOCAL\" \"$REMOTE\" \"$MERGED\"

Since Charles Bailey never answered how I should give him credit for this, I hope this is an appropriate way to finally close this question.