This is just a curiosity question.

Has anyone had to accommodate/provide closed-captioning on a piece? If so, how did you do it?

It depends on what the duplication or post house wants. I have provided just typed sheets and others have wanted word files etc to import into their software. It is then encoded and inserted into blank lines in the vertical sync.

Jeff

If you go down the MPEG2 route (for DVD for example, or
digital sattelite distribution) it is encoded (digitally) within
the MPEG2 file. I don't think I've seen software encoders
who can embed this signal. A DVD duplication house might
know more about this issue. If you want to know more for
mpeg2 encoding I might be able to ask some friends of mine.
Lemme know if you need it.