If you're wanting to somehow "spoof" a users address bar, I'm afraid you're pretty much out of luck.
AFAIK htaccess is good at allowing alternate URLs to work. eg.
example.com/real_but_ugly_url.php will still request the same file. The difference being that "pretty_url" can be used in links.
I think if you want to retain "pretty_url" displaying in users address bars the way to go is not with htaccess but with server side routing.
Browser security measures are in place so that "where the address bar says it is, is really where it is"