I see... I'll do some more google-fu and try to come up with an easy solution. I can always record the playback with audacity, but I will have a messed up recording if there is any rebuffering needed, or the movie skips around for any reason.
Why do I want just the audio? Because there are some awesome unofficial remixes/tracks out there that I want to burn to CDs, or put on an mp3 player, etc.