I donated my 8 frame hive to a friend that has 10 frame styro equipment. (He lost his package in shipment)

He has plastic frames and starting brand new he has no comb and I have no foundation to work with. I am not thrilled about plastic frames but I was thinking I could build some comb for him by using his boxes on top of my hive. So the question becomes how do you stop up the two frame gap that would be at the bottom of the first super?