How can you use one NetStream to publish video and audio from another NetStream in AS3?

Let's say one of your client programs in AS3 is able to receive live video and audio from a NetStream and play it on the screen.  How could you make it also take that video/audio stream that it's receiving, copy it over into another NetStream, and publish it elsewhere?  I need to know how to do with this regardless of whether RTMP, RTMFP, or some mixture is involved.  The reason why the stream needs to be relayed this way is a real long story, but it's necessary in this particular case. Thanks!