As far as I've ever heard, you cannot stop it from trying to connect. I am under the impression that it downloads 10 WUs and after crunching 7 of them it will try to talk to the server to get more.
Why do you need to disable it from asking for more work?
How about telling it to ask before connecting to the Internet? That should stop it from connecting. Failing that, how about blocking FAH behind a firewall until you want it to connect?