That's a pretty stupid requirement. The stats collector socket is bound to itself, so it's inaccessible from anywhere else (on machine or off) regardless of firewall settings. There's no need to worry about it, and no there is not a provision for doing it via unix socket instead.
Indeed it is a totally harmless thing and the request makes little (if any) sense. I will pass the answer over and I do share your stance regarding excess in paranoid modes :)
Can you create a virtual network interface, assign an address to it and have PostgreSQL listen to it in addition to the socket? I'm thinking not the eth0:X type but potentially what VirtualBox (vboxnet0), VMware (vmnet0) or other virtualization products do using brctl.
