That would work, the callback will be handled right there. If you need the data in the RTMP provider, which you might, you should leave the forward mechanism in place and handle the data that is returned in
com.longtailvideo.jwplayer.media.RTMPMediaProvider.as in the onClientData. You have to add a case to that function.
With JW Player and Flash Builder, it is fairly painless to step through this with the debugger and look at all the data that is available, etc.