Leave the account for few months. The IP and other data will be removed automatically since there is a certain period of time and after that all data will be wiped out from the database.
if this is authoritative
https://bitcointalk.org/myips.php I would say that the IP address is remembered only for 30 days. at least that's how I see it for my account.
I'm very curious, about what kind of trouble connecting an IP address with an account on the forum can cause?