How can I set my discount code to work only on pairs of items?

[SisterSisterCDN]

I created a sale code so that if people buy two items (mix and match of a toques + totes) then they save $5 on each. You'll see this advertised in the banner at the top of my site www.sistersister.ca

The problem is that I don't see a place to indicate that it has to be in sets of two as right now it's showing 2+ qualify. I see a place to limit one sale per customer but I don't really want that. I just want the coupon code to work when purchased sets of two. So if they buy 3 they'd get the discount on 2 but they wouldn't get a discount on the 3rd item until they bought a 4th. Is there a different coupon I should use, or is there a way to tweak the code of this coupon to only work in sets of two?