Creating accounts using proxies and vpn should be disable abusers will surely use vpn and proxies to bypass this evil ip payment to create more multiple accounts to abuse bounty there might be already a vpn tagged with evil ip but there's so much vpn and proxies available out there they can just switch one to another.
I'm pretty sure there is a way to figure out when someone connected thru vpn/proxy
maybe the packet data received/sent from those IPs has certain marker or header
or the forum could just use third party service to build and update blacklisted vpn/proxy IPs