Setting it to stream would accomplish the opposite of what he wants, which is for the sound to run independently of the timeline.
Darius, just put the sound on the timeline and set its frame properties to Sync: Start and Loop. That's for an AS3 document. For a Canvas document Start sync isn't available, so you'll have to use Event, which works just as well, but will cause a new instance of the sound to start playing over the previous instance if the timeline ever loops back to where you start your sound. So you'll have to make sure that doesn't happen.