No, don't think there is a way around that. You can set the forum to approve registrations and that can reduce the rate of the registrations from previously banned members.
Cheers, thought that would be the answer, unfortunately the forum is very busy and no one has enough time to approve all registrations really!
Can you set it send a confirm email automatically to confirm registration and ban people by their email address? That way people would need a genuine email address to sign up!
Yes, you can configure the forum to validate the email of the member before allowing access. In the Email Server Configuration page, set Email Validation to On.