Streaming audio/video W/ MS Proxy 2.0 & HTTP

["Mack" <mack () mack com>]

We allow certain people in our organization to have web access through MS Proxy 2.0. We only allow HTTP through the Web 
Proxy Service. The problem is some people are figuring out that they can get streaming video or audio by using HTTP.
 
Does anyone have any idea how (or if) I can filter this streaming audio/video without stopping HTTP access altogether? 
If possible, I could restrict access through the proxy server or a Cisco router access list? 
 
I currently do not have the Winsock or Socks service enabled and would prefer to keep it that way.

 
Thanks,
 
Todd