So they are force you to spend your own money from a bitcoin client in their favor.
They could double-spend transactions to you, but they couldn't redirect your transactions from one Bitcoin address to another one. There are much easier ways to "surround" someone if you control the ISP.
Seednode bootstrapping is used in Tor, I2P, GNUnet, and Freenet. Just removing IRC and using the already-implemented seednode system will work fine.
That's just one method of finding your external IP. There are also two HTTP external IP services.