Here is an example that could be useful for you:
You would basically attach an event listener to the movie clip.
The example above shows you how to attach click events but the same logic could be used for any kind of custom event.
Try adding the event listener on the systemManager.
If this post answers your question or helps, please mark it as such.
Greg Lafrance - Flex 2 and 3 ACE certified
Flex / AIR Development, Training, and Support Services