“sold individually” for some variations only

I have a very straightforward scenario:

We’re selling music on our site. Physical CDs and digital downloads. Each album is a product with variations, allowing the customer to either buy the physical CD or the audio downloads. Obviously, we would like to allow quantities to be selected for the CD, but would need a “sold individually” option for the downloads (you wouldn’t buy multiples of a download).

So the question is, how can I bring the “sold individually” option into the variation level and select it only for some variations, same as the stock management?