Here's a thought, maybe trying for technical solution is too hard, why not try a little bluff....it has worked for me in the past.

This assumes you have a current and active e-Mail for the weasel that is causing you such a headache, and is suggested in ignorance of what he is actually doing. However try a legal threat, advise him you utilise I.P logging, that you have I.P tracking software e.g Visual Route and that you will advise his ISP of his activities and that they will shut down his account, if they are a decent ISP they will probably do just that if you write to them politely informing them of his activities.

Additionally you could threaten direct legal action if he is breaching published terms and conditions of use of your site.

He/she may be a computer wizz but it is unlikely they are also a legal guru, so it may just work, like I say it has for me.

Anyhow just an idea !!

Best of luck, you have I am sure the symapthy of every self respecting webmaster.