The Kuat NV like mine does not have a rear cup. The Kuat Transfer mentioned by the OP has a very small rear cup with a strap. You can notice on their website demonstration the guy barely pulls the strap tight. As others mentions you could probably leave an air gap. For the Flo 60s on the NV I have to pull it tight because the strap is almost too short, but I have never had an issue and there are no wear signs on the wheels.

https://www.kuatracks.com/product/transfer/