Adding audio to a h264 or Flash file

is there a way to add audio ONLY to an already compressed file without re-compressing the video?

30s web commercial that is currently in h264 & Flash file types only. Audio that needs to be added is 4 seconds (aiff).

""" What you do with what you have, is more important than what you could do, with what you don't have."

> > > Knowledge + Action = Wisdom - J. Corbett 1992 """"

Yup. This is trivial. Just remix a new soundtrack without picture, and combine the existing video track with the new audio track using Quicktime Player.