I also needed this requirement and got a similar reponse to you. In the end, like so many other things, I just found a work around. I mostly got url rewriting working in webgui with an HttpModule but then I still had one issue left that I finally gave up and just made that part of my app not using url rewriting.
It doesn't sound like you need true url rewriting like I needed. Instead you just want to remove the url parameters from a link in an email? Couldn't you just have that link point to an aspx page that strips the args, puts them into the session, and then redirects to the webgui page with no parameters?