Redirect based on Host Header and Hide URI?

You could probably hack up my ProxyPass iRule (posted here) to do just the initial redirect pretty easily, but then you get into issues of relative URLs, etc. Let's assume a client hits http://app2.example.com/ and we don't send a redirect but internally map them to app2.example.com/dir1/index?id=1. Now imagine if there was "logo.jpg" on the app2.example.com/dir1/index?id=1 page. The client would request http://app2.example.com/logo.jpg, but how should that be translated, if any, on the way through? Should it be http://app2.example.com/dir1/logo.jpg?id=1 maybe? Or just http://app2.example.com/dir1/logo.jpg?