Temporary IP ban on banned user logout/register

[dirgotronix]

I have a few users that I have banned, and the usual activity is that they'll log out and try to re-register. If there could be some way to automatically ban the IP address they were last on from registering, and then un-ban it X minutes later, I would be very, very happy.

I've seen the no logout hack, but the problem there is that a few of these people use public PC's, or try to log in at friends houses.

To recap:

Banned user logs in, sees no-permission. Logs out. Forum checks the ip, adds it to a temporary IP ban table.
User tries to register, gets the ip ban, gives up and goes away.
IP ban goes away after say, 30 minutes.

That would make me happy.