Is there a way to handle Print Units within ShootProof?

For grad packages where a print unit could be multiple sizes, is there anyway to handle this within packages?

For example, an order might include 4 units. Those units could be any combination of (1) 8x10, (2) 5x7, or (4) 4x6, for example. 

The only thing I could figure out was to make a Product which was  “Print Unit” and allow so many of those units in a Package. This tells me what images they want, but there is no way for the client to enter the size. I also need to be able to restrict how many poses they can order from. Ex: 8 print units from 3 poses is a package I offer.

Anyone have any ideas for how to make this smoother?