If you send an HTTP redirect, the client will see the change in their address bar. If you rewrite the URI and/or host before sending the request to the server, the client will not see the change. So in concept you could modify the ProxyPassv10 iRule to send a redirect instead of rewriting the URI, but you'll need to strip out a fair amount of code related to the rewriting. You can send a 302 redirect with HTTP::redirect or any HTTP response with HTTP::respond.
http://devcentral.f5.com/wiki/default.aspx/iRules/http__redirect
http://devcentral.f5.com/wiki/default.aspx/iRules/http__respond
Aaron