Servers harrassed by individual on constantly changing IPs

Instead of blocking it, you can employ a different approach - I think I heard it on one of the SO podcasts, and/or maybe SO use it as well.

Do not delete the account and the posts - just make them visible only to this account and noone else. The kid will continue to try while you play his game. If he sees that his comments are not deleted, he may loose interest. You can leave the comments visible for the entire 92.x.x.x subnet, with the hope that he'll never notice, and you will not offend other users.

If it's available you could try having to approve new accounts or approving the first post of a newly created account.

I would try and trace back (tracert) one of the IP addresses to the provider, look up an abuse contact email/number for the provider, and report the IP address.

If the user is on a public network you're pretty much at a dead end, but if it's a company or residence then you might be able to request an inquiry into the IP Address ownership.