uhhhhhh.... why?
i use mod_rewrite on a company intranet site to send all requests through a filter to see if they can access it (including file downloads..)
so if someone did something like this:
http://intranet/earnings.txt
it would redirect to
http://intranet/filter.php?url=earnings.txt
and if they were cleared it would send them that file.
what you are talking about using it for is already handled very well by php and is not necessary.