Here's my use case:

Let's say I have a "free" and a "paid" version of a node that I'm creating. I can't complete the "free" version checkout because PayPal requires a value of greater than $0 to complete checkout. Therefore, I only want the "paid" version, that is, the version where you select the "paid" attribute, to get dropped into the shopping cart.

I KNOW that I can create a whole second node type and have just that one get put in the cart, but for other reasons I would greatly prefer to keep all this one node type. Is it possible? Is it just a Rules thing?