If you're referring to what the remote web server sees as your REMOTE_ADDR, then I'm pretty sure you can't do what you want. AFAIK REMOTE_ADDR is set up on the server to be the IP address of the remote connection - as determined by the tcp/ip stack - not by any data sent by the remote system.

If the remote system (from the web server's point of view) could set REMOTE_HOST, they'd be able to spoof who they were.

If that's what you're trying to do, stop it.

:^)