[Anais9000]

I think we've finally got the answer to this one, Doctor!

In the html fragment editor, check the whole code box. Then click the find button, and do a find/replace using
bdn__ changes into BdToc_

Notice that the the first string has 2 underscores at the end, and the replacement string has only 1. Also, type upper/lower case just as shown.

This seems to be some kind of undocumented BD setting, which does exactly what you describe you want. I would still like to figure out how to get rid of the underlines in the TOC itself; I also don't think I'm going to use this method because the highlighting of the chapter heading only happens on the first line.

EDIT: Actually, I'm wrong about that. It seems to highlight the whole chapter heading. What's more, you can underline as much or as little of the TOC entry as you like, by shifting the </a> over to the left. For instance, instead of:
2. &nbsp;The Harrison Street Police Court</A>
you can have:
2.</A> &nbsp;The Harrison Street Police Court

So this looks like a complete solution, finally!