In the filter window, on the lower left side you will see a section for Logic, and can choose from "NOT group," "OR group," and "AND group." These allow you to make power filter combinations.
By default, filters you add create an "AND group."
You can click on "NOT group" on the left to add in a layer that tells the filter, "find me everyone who is NOT this." Pair that with the "AND groups" or "OR groups," and you can filter out virtually any combination of volunteers.