When setting up a minimum order for a coupon, is it possible to designate that the minimum order be from certain categories only?

In other words, what I want is a coupon for a customer who spend $40 in categories A and B, that will let them save $15 in categories A and B. (However, the coupon would not work if they spent $40 in categories C and D).

Is this possible? It seems right now that all I can do is restrict the coupon itself to categories A and B...so that they could use the coupon if they spent $40 in ANY category, and that's not what I want.

Any thoughts?