We have a policy that no one feels empowered to enforce, is what it seems to me is the problem.
I don't think the problem was that we didn't feel empowered to enforce the policy when mieskie first came on the board. I don't remember a single negative word about JoeAverage being stomped, and there were only a couple of folks speaking in favor of mieskie when he was originally stomped. We did identify at that time that there were things we could have done better with in the situation - sending the warning by e-mail, making sure the person warned knew it was official, telling the person that it was being discussed in Bureaucracy.
I think the real problem was when he came back, and we had no sure way to prove that it was the same person. A good number of people were sure it was him, another group was just a vehement that it wasn't him, another group said what does it matter, he's changed anyway, and another group went into hiding.
There really is nothing you can do about that situation. We have set the burden of proof for identifying an imposter very, very high. If the guy wants to post badly enough, he will. You can ban everyone from the guys e-mail domain, but what if he uses Hotmail? You can try to block the IP address, but that runs the risk of blocking innocents. Back when they were working together, it would have been impossible to block Darth and not block Cybervixen.
I don't think there is anything wrong with having the original policy enforced by the stompies, as long as the specific formats of e-mails and warnings are worked out. OTOH, I'm not sure there's any way to devise a plan of action ahead of time for what to do when a suspected imposter arrives, and tries to fit in. If an imposter repeats the same behavior as before, you just stomp him the same as before, but if he's not misbehaving, and you have no direct proof it's him, what CAN you do? Fortunately, I think it will be a rare event.