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Have you checked out the banning of ip address' to your site from the admin menu->system admin->preferences->general settings
Enter IP addresses that should be banned from the site.
Separate each with a |, case insensitive, regex enabled.
^aaa.bbb.ccc will disallow visitors with an IP that starts with aaa.bbb.ccc
aaa.bbb.ccc$ will disallow visitors with an IP that ends with aaa.bbb.ccc
aaa.bbb.ccc will disallow visitors with an IP that contains aaa.bbb.ccc
This approach seems to accomplish the same thing as what you were wanting to do, with less maintainance. Just a thought....
Hope that this helps,