1) Enable insim ( /insim 29999 in command line or start cfg file..)
2) Enter details (IP address etc) in the INSIM RELAY tab on the Racers and Hosts Online window in LFSW (http://www.lfsworld.net/)
3) Enjoy!
This could work be it not for a check i added lately to prevent crack-hosts from using the relay. A host must be known on the master to be accepted by the relay. A LAN host therefore will not be accepted I'm afraid.