You don't have to have a static IP. You can set to a different port than the default of 6346, but that's a hassle.

Sounds like your ISP is attempting to control filesharing, so keep at them. Ask them how they can set it up to allow you a clean connection to the Gnutella network. Perhaps they can route you to a different 'hub' or give you a different cablemodem.

Search for posts containing the word "Sandvine" for more discussion about ISP's using filesharing controls