Is there a way to control which lines within an AP invoice a payment term discount will apply to?

We have a client requirement coming down from the state controller that any state fees being collected are not subject to available discounts.  For example CA Tire Fee is a flat $1.75 on every tire bought.  We have an established discount with the vendor that is to apply only to the cost of the tires themselves.  The invoices would have the charge and fee on separate lines, but the way it is working now is the discount is calculated on the entire invoice.  We are looking for a systematic way to control which lines are applicable to discounts.