Ah. Well, I'm guessing I can figure out the jquery/javascript, I just hadn't figured out a place where I had access to the client side events. I'll go back and take another look (although if you have any more detail about *where* that javascript/jquery would hook in, that's be great!).
I did suggest to the owner of the site that they might switch their configuration to a single drop down with the various choices, but that was a somewhat hesitant suggestion, because even with the test setup they had, the total # of choices was already about 15-20, which seemed a bit high to me (their original config is actually a "parent" choice, and then two drop down boxes, one with I think 5 things in it, and one with 3 - so 15 combinations total if the parent is set to "yes" - so 16 total to convert to a single set of choices when the "No" is included.)
Thanks for the help!