[videoRx]

Looks like I was able to figure out a solution based on FFmpeg alone. It appears that, when FLV is the published format (-f flv) for RTMP live publishing (output is set to an RTMP URL), that you can override the videodatarate and audiodatarate values of the NetStream.client.onMetaData() info object by simply specifying a video bitrate (-b:v) and/or audio bitrate (-b:a) and so long as you're only copying the respective tracks (-c:v copy -c:a copy or -vcodec copy -acodec copy), you can override the published values to an FLV container. Good enough for this problem!

UPDATE: This only works with the latest builds of FFmpeg. I compiled directly from the GIT repository.