Well, here's an idea. Give sysops emergency power to ban a logged-in user (by name), while simultaneously blindly banning their IP address -- temporarily. And they'd be honor bound to report the ban to the list, just as when a sysop protects a page to stop an edit war.
It is better than nothing but why not keep it simple?
Show the ip-adress of all users to sysop's and give sysop's the power to block them.