Sync inventory between same product, multi variants?

Any thoughts on how to manage a product that has multiple variants?

I have a product that I sell as single units, and as a pair. It is the same product, in the same listing, and the quantity can be controlled by ordering as a singles or as pairs. There is a specific reason why we sell in both single and pair that needs to remain.

I looked at using some of the inventory syncing apps (SimplySync was one) but they want to sync the inventory by SKU. So if someone buys a single, it drops the inventory for Product X by one unit. But if someone buys a pair of Product X, it still only drops inventory by one unit. Thoughts?