I've run online services on the net for about 10 years now and prior to that I ran standalone dial in systems, all multi line, chat enabled, etc.
Assuming he's like the people I've had to deal with in the past then he will not go away until something else takes up all of his time and even then he will return back here from time to time.
I had people show up at my office screaming and yelling and threatening because they were banned. One guy left a 45 minute message on the companies answering machine that I wish I had saved because it was classic.
He started off in this calm collected voice expressing his concerns and as he went on his voice got louder and louder and more insane and by the end he was screaming and cursing and banging his phone receiver against things.
These type of people are a fact of life and banning is very hard due to proxy services, open proxies, ability to change iP address at your isp, endless free disposable email accounts.
You can block people coming from IP addresses of known open proxies by enabling the system at
http://www.spamhaus.org/ , it's free to use as well but am not sure how hard it would be to work into AZ's system.
Other than that your limited IP bans but the problem there is you'll effect more than just him. You can cookie ban but they can easily be erased.
Using a flash cookie on a alternate domain worked pretty well for us in conjunction with the proxy blacklist but nothing is 100% and if someone is determined they can always get on. They'll walk to the local library or wifi hotspot.
What I've found is you make it to where it is a pain in the ass for them to do it and they find somewhere else where it's easier and then leave you alone lol.
What is also a good system is one like Slashdot where the users moderate themselves and if you get moderated down then your posts fall below a level that most people have set and you basically fade away. The people can still make new accounts and act like tards but fellow members tend to put the smackdown on them rather fast. It's kind of like AZ's rep system but it's tied into user levels and filtering.
There are some crazy crazy people out there.