TOPIC: Event Packages - Register for 6 out of 12 classes

I've got a client who is putting on a series of classes. They're selling them individually, but they also want to sell a package of 6 classes. Ideally this would be a single purchase and the user would just check the boxes next to the classes they want to attend (list set up in custom fields). The question is, is there a way to specify that they must choose at least 6, and only 6, of the classes?

DTRegister 2.6.9 on J! 1.5.23.

There is no way to specify that at this time.