Sending to members of one list who are not members of another

I use Mailpoet to generate my free newsletter sent to my “Subscribers” list, and to track email addresses of customers who have purchased my product on a “Customers” list; many of whom are also on “Subscribers”. I would like to be able to send special offers to “Subscribers” who are not “Customers” yet. I don’t want to spam customers who have already paid for the product, with these offers.

At the moment Mailpoet can send to multiple lists at a time, but is there a way to send a newsletter to members of my “Subscribers” list while excluding those who are already members of my “Customers” list? (i.e. Subscribers && !Customers)

thanks,
Graham