Where do you live and who is your ISP?
I live in Ontario, Canada. My ISP is Rogers.
This kind of thing has come up before, and in every case that I can recall, it turned out that the ISP wasn't really combating viri but trying to clamp down on Bittorrent or some other P2P tech that takes a lot of bandwidth. They can't really say it that way, though. Why would your miners be consuming a lot of bandwidth? You should only have one that is 'net facing while the rest just connect to each other and that one. If nothing else, you can port that one's connection over Tor, although that will slow things down. A ssh tunnel to an off-isp-network shell account would work well.
Ok I have 2 computers with 5 miners (cards). I use Deepbit and GUI miner (used to use POCLBM but switched recently). For the last while I have been running only one computer which has 2 miners. My question to you is: does the mining software take a lot of bandwidth? I can't imagine it being more bandwidth than downloading a torrent. Also, will porting through the TOR network really hide the packets from my ISP? I never had a use for TOR so I am unfamiliar with it.