Is there a way to do a balance comparison on only line items of a certain type, e.g. products?

I have set up a rule where I do a balance comparison on the order total, and offer a free shipping service if the order total meets that criteria.

Unfortunately, the rule is calculating on all line items, including shipping, and offering free shipping when it shouldn't.

For example, let's say I offer free shipping over $25.00. The order total comes to $24.00. The customer chooses $5.95 ground shipping and gets the checkout confirmation page. Then the customer goes back to the shipping options page. Suddenly free shipping is an option because the order total is over $25.00 with the shipping charge.