IP ban from registration only

[Hoth]

The problem with IP bans is their tendency to lock out innocent posters with the same ISP... or in some cases, even innocent posters using the same computer as the guilty. With this in mind, I prefer to have IP bans only block registrations, and not block people from posting -- if I didn't want someone posting, I'd have banned them the normal way already. Losing a few people who could've otherwise registered isn't nearly as bad as locking out valued existing posters and making them think they've done something bad.

Stated simply: I'd like a modification to the IP ban system which allows all current users with the banned IP to continue posting as normal, but continues to prevent new people from registering from that IP range.

If someone could give me an idea of what file to look in, I could probably do this... as of now I've no idea where to look though.