That's what I was saying.
You cannot currently move/animate the physical layer.

You must use an image sequence.

So, in Maya, you would:

1. Place your "displacement" emitter in the same location as your exahust emitter.
2. Group, and/or parent it to the exahust emitter.
3. Render the image sequences out separately.

Then, they will match up in post.

Once I get off vacation, I'll ask kevin if this can be my next video/html tutorial, so that way I can better explain what I mean with this technique