As much as I hate to say it, even an IP ban won't stop it. You can easily jump on a VPN that will assign you a different IP whenever you want. The only way I can see this truly getting fixed is either:
1. Limiting Trail Accounts even more.
2. Get rid of the Novice Network Chat.
Those are the only two that I can see that will absolutely stop this. Both of which probably wouldn't be a great idea.
It's this kind of stuff that has kept me out of NN chat since the beginning. My first and only experience with the NN chat for me was people talking about how what time of the day you shower gets you laid more... That is the kind of chat that belongs in private channels. Just my two cents.