I know what you mean. There is not much of a concern for it, and even the best program for the ATI HDTV card (WatchHDTV) does not support captioning because captioning "isn't high on his list of priorities." It's a hobby with him and he IS doing it for free, so there is not much one can say about it.
Well, you can try and play around with Graphedit. I did, but I couldn't get it to render ATSC captions, but the analog captions look like they might be easy to fool with. I don't have an antenna or cable attached to my analog plug in my computer so I don't know exactly how to tweak it.
There is a thread
here, at Rage3D that explains some about Graphedit, and there are a bunch of layouts and examples to use. There are several setups with closed captioning.
Have you tried that?