flexible strippenkaart

Within my dog school, many people train with multiple dogs. In addition, we offer disciplines where different rates apply. I would really like it for clients if I could offer a strippenkaart where the number of strips can be set for each discipline, so that they do not have to purchase a separate card for each dog AND each discipline.
For example, an obedience class of a cheaper rate, could be taken off the same strippenkaart as a specialized (more expensive) discipline and private lessons could also be booked off this card.