Does anyone know of a utility (preferably command line based, double preferably something that will run on Linux) that can concatenate two AAC files into a new file?

I recently read that Doug Kaye from IT Conversations is considering dropping support for AAC/.m4b versions of his hosted shows due to problems finding a good Linux encoder. So I emailed him and recommended FAAC, but it turns out that his problem is a little more complicated.

Essentially, he wants to be able to encode all of his shows in AAC format once, then use a utility to add in announcements/advertisements/whatever. He already does this for his MP3 format audio, so I suggested that he transcode from MP3->AAC. But since he has 800 shows that might need to be re-encoded on a daily basis, this isn't very practical.

Google didn't really turn up anything, other than 1 Mac OSX application, so I thought I'd check here and see if anyone knows of a solution.