TraFFikko: Well, what you need as far as I know, is a firewall capable of dynamically altering the IPtables/IPchains on the fly. Doing this is well beyond my abilities, but you will get *some* information from Googling, and I'm sure there are other related threads here on LQ.
Don't quote me, but something like Guarddog or Smoothwall *might* be along the lines of what you seek.
Sorry I can't help on this subject, but there are some very able people around here and hopefully one or more of them will pick up on this and be able to offer some good advice.
Best of luck!
P.S. - You would do well to post in the Networking forum.