Customer Exemption Challenge

Client has requirement to establish customer site level exemptions with one caveat - a given customer could have 50 - 60 sites and maintaing the exemptions at the site level would be a extremely cumbersome.  Customer coule issue an exemption certicate for a state that may apply to 10 of the customer sites and setting up the exemption for each site require to much maintenance.  Looked into setting up a Party Level customer exmeption but do not think this can be setup for inividual states.  Can anyone think of a way to handle such a requirement at the Party Level?  Any help would be