JCO destination gives ip adress of server instead of hostname.

We are connecting to a 46d system with a web dynpro application (with WAS 7.0) from a different location then the 46d system. The problem is as followed. When i test the JCO Destination, the message server (PUBLIC group)responds with an IP address where the JCO can connect to. Because the addresses are being NAT the from IP is different then the destination IP. The message server response an IP of the backend system. Now the JCO Destination test tries to connect to the IP address given from the message server. The JCO is not able to connect to the IP because of NATing. I just want the message server to respond with an hostname instead of an IP address. Is there a way to solve the problem? Thanxs in advanced. Jeroen