Hook for IP Blocked guests?

[findingpeace]

What hook would I use to create a plugin where the guest's IP is blocked under User Banning Options?

My problem is that I've implemented a cache for guest users that works great, unless an IP blocked guest views the site when logged out, in which case two bad things can happen:

1) They see the cached version of the site, like they aren't blocked
2) They happen to be the cache changer, in which case everyone else sees "Your IP has been blocked" for two minutes, which is obviously really bad.

As a solution, I thought I'd use a plugin to set a cookie for the IP blocked page, and then have .htaccess never cache when that cookie is present.

Thanks!