Ugh. don't do that. if you /must/ have a system like that (and it's never a great idea) keep your private keys on one box, and enable agent forwarding. It's not as good as just enabling the one-way ssh, but it's not nearly as bad as scattering your keys.

Why does everyone seem to think it's okay to build a system where any one compromised box can compromise the rest of the system? this 'jelly doughnut security' is really popular among the PHB types, because it's easy, but it just seems really, really dangerous.