Twilio developer evangelist here.
You can insert the fork stream widget into the Studio flow that leads to a Flex agent?
[edit]
As requested, the media stream should join when the call is accepted by an agent. I don't think you can do this in Studio, so you would have to implement this as a Flex plugin. When the plugin detects that a call has been accepted by an agent it could make a request using the call SID to modify the call and inject the <Start><Stream>
TwiML.
I don't have more detail on that right now, as I've not built that sort of thing myself. Let me know if this helps.
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