I got an email from Phil Weber who had an interesting solution to the __doPostBack problem. He used JavaScript's function pointer support to redirect __doPostBack to a function of his own creation. In this function, he can add whatever functionality he wants, including a call to the original __doPostBack method. And what's funny, like me he was having an issue with a rich text editor. What is it about rich text editors? (They're non standard, that's probably what it is).
This is a pretty elegant solution. Especially since his solution can be enabled on a single page as needed. My solution processes every page output from the site. The primary benefit of my solution is that it can add the additional code directly into the __doPostBack function, which means I don't have to replicate the code to get the "theform" instance. Also, since it automatically fixes up every page in the web app, I don't have to remember to turn it on in every page.
If you ask Phil nicely, he might send you his code. If we all ask him nicely, maybe he'll post it.