[Exim] HOW TO RELAY TO NON-TRADITIONAL PORT

Installed exim 4.10 last night on a FreeBSD 4.6 box with the following
"send_to_smart_host:" configuration:

send_to_smart_host:
    driver = manualroute
    route_list = !+local_domains 192.168.181.1
    transport = remote_smtp

This works fine, however, in order to relay to an ISP SMTP server though
a SSH tunnel, I need to connect to port 50000 on 192.168.181.1 and not
port 25.

I cannot find how to do it on the documentation, the FAQ or the
discussion groups.

I have manage to accomplish the same thing by proxying (Delegate proxy)
port 25 on 192.168.181.1 to port 50000. Although it works, I consider
it a kludge and would prefer to do it the exim way.

Any and all help are gratefully appreciated.