Well, this is really weird but sometimes the option is there and sometimes it's not.
Here's proof - look between "Reset Plays" and "Consolidate Files":
So the real question is how to get that to show, and I can't say for sure how I did it. The trick seems to be related to whether the episode is selected or not before you right-click on it, but that's not entirely it. I think what I did was click on an audio file, then right-click on the video file while the audio file was still highlighted.
It may be easier to just open the video in Quicktime Player, and use that to export the AAC audio.