I have been pondering ways to ban users which would be resistant to creation of new accounts and usage of different IP addresses. Prose analysis/stylometry comes to mind. Tor Browser can route your traffic through an exit node, prevent JS, genericize user agent and plugin availability, etc, but there's no protection against the way you write.
Though I prefer to stay out of forum drama, I will weigh in on this from a technical perspective. The user in question appears to have a particular writing style that a wonder if could be analyzed by some sort of algorithm, and it appears that such software does exist. They write very long posts, which could be extremely useful as sample data for a system such as JStylo.
While I personally do not have a problem with this user, if it the wishes of the moderators to ban him rather than his accounts, this might be something to look into.
Somewhat Orwellian, though. Perhaps he's best left to do as he will and ban him as the need arises. That would be my personal suggestion. Stylometric banning would have to be much more necessary, in a last resort scenario, for me to truly advocate its use rather than simply musing about it.