Sorry to tell you, but....
There's no way to do that. Your IP address is required to send information to your machine. It's like asking for letters but hiding your mailing address. Your IP does not personally identify you, and is not a security risk. It's simply a numerical value used to route the packets (Kinda like letters) to your machine.
Most "IP Blockers" are simply bouncer machines... machines you run your connection through and get to use their IP address. However, even in this case, your ip still has to be visible to the bouncer machine (more technically called a proxy).
If you're really concerned about privacy, you may wish to try Tor:http://www.torproject.org/
- My statements do not establish the official position of Microsoft Corporation, and are my own personal opinion. (But you already knew that, right?)