What a great question. I hope someone can point you to some answers. Farming this out to a service house is likely the best / most immediate solution- unless you have time and are willing to invest in equipment and education. Below are a few informational links for your reading pleasure. I wish I could offer more help:
The ATSC standard:
http://www.atsc.org/standards/a_52b.pdf
Misc informational links:
http://www.tvtechnology.com/features/audio_notes/f-TC-metadata-08.21.02.sht...
http://www.tvtechnology.com/features/audio_notes/f-tc-metadata.shtml
http://www.digitaltelevision.com/dtvbook/ch5.shtml
Jim Krause
tabletop productions
http://www.ttop.com
(812) 332-1005