I\'m using mod_rewrite to rewrite pretty URLs to a form supported by a Spring 2.5 application.
e.g. /category/cat1?q=x => /controller?category=cat1&
Is there a host header you can use? Sorry for being so vague, but last time I had to do this was using PHP (urgh, dont ask), and I think thats how we did it - eg REQUEST_URI (http://www.askapache.com/htaccess/mod_rewrite-variables-cheatsheet.html)
You also may be able to SET a host header in the rewrite (http://httpd.apache.org/docs/2.0/mod/mod_rewrite.html)
eg:
ReWriteRule /category/(cat1)?q=(x) /controller?category=$1&q=$2 [E=FOO:....]
(and no, I'm so totally NOT a mod-rewrite ninja)