Hi Rob,
I do not recommend the second option (using htaccess) it's a worse abuse of Apache than described above as it would have to do that for every file request (gif|html|js|css|etc)
So my solution for you is to httpd.conf and RewriteMap either by using prg: map or txt: map.
my recommendation will of course be prg: map where you can query your database
For your help http://httpd.apache.org/docs/current/rewrite/rewritemap.html
Cheers!