two way communication with server using flashvars

In Maple TA, an e-learning environment, flash movies can be used for questions. All communication can only work via flashvars. However, the flash interface has been developed for AS2. In AS3 it is not a problem to pass the flashvars variables into the Flash movie. To send the scores to the server using Flashvars seems impossible. I can't figure out how to use the ExternalInterface to send the response to the server. I have no control over the server side, flash movies can only communicate via Flashvars. It seems possible in Moodle, so I hope someone can help me.

Harry