Not to be snarky, but that's easy. Just disconnect your cluster from the internet. We have hundreds of customers that are running disconnected clusters.
Haha. I still work for Red Hat, and Consulting at that. My pay is determined by how many billable hours I put in and my customer reviews. Not directly by how much you buy.
Not complaining - If you want me to complain about IBM cluster technology that would be a whole different story.
And no I'm not gonna ask about disconnected clusters :).