The sister program to rtmpdump - rtmpgw might be a better option as you could then use your existing generic site-util and have rtmpgw send the rtmpe stream to mediaportal as a regular http stream.Well, It seems doable, and as I understand it's using RTMP://, and that's why you can't find it using fiddler (it only captures http://).
But as the generic site-util doesn't support extended rtmp urls (with swfvfy, auth etc) it should be coded in it's own util, which shouldn't be hard given the steps described at the downloaders_wiki.
So... any volunteers?
More info here: RTMPGW(8):
Also, the rtmpdump devs are usually pretty quick to respond if you post to their mailing group with any questions: The rtmpdump Archives