Friendly URI Re-Write based off of User-Agent?

So, currently you are sending back a 302 and want to make this not occur my pre-empting the destination that they will be redirected to and instead rewrite the incoming request? So when you say "The application to not see the redirect" you mean "The application to not need to provide the redirect", right? So what does this not satisfy?...

when HTTP_REQUEST {
      if { (string tolower [HTTP::header "User-Agent"] contains "mozilla") || (string tolower [HTTP::header "User-Agent"] contains "testagent") } {
             pool aaa
             HTTP::header replace "Host" "url2.domain.com"
      } else { 
             pool zzz
      }
}