It depends upon how they use the program. They might only be using it to scan along a particular range of ports known for p2p sharing. The open range ports I'd suggest trying are (49152 - 65535). You might also try ports 1111, 3500, 443 & 80. Go to LW's menu bar, Tools>Options>Advanced>Firewalls & that's where you can change ports.

I don't know if proxies can beat such programs but worth a last ditch look at if changing ports doesn't work. A Fix for those whose ISP's block Limewire pages 2 - 3 which have links to alternative instructions. The post in the middle of page 2 has some very good ones.