Well, a McGyver way of doing it might be to get an RF jammer and a very highly directional antenna and piont it twords ISPs AP. One for each IP you want to kill. It will keep triggering their it's CCA and effectively disable it. Maybe students clients will not try to associate to it any more or they'll probe for it like crazy and you'll have a different kind of problem.
The other thing that you can do is get some equipment you can set-up to keep disassociating clients from ISPs SSID. IT can be done, just not cheap and not usefull.
Both of the solutions aren't great. Some vendors like AirMagnet or AirTight have equipment that you might use for this, however I doubt it can do waht you want.
What kind of filter do you have set that it can be bypassed by them?
