List price is the same for summer and all seasons for the 18" wheels, once you agree on a price for the car, make the tire swap at no cost the item that will finalize the deal and sell the car.
I would expect that they would jump on that to move the car.
Didn't you guys just get dumped on (snow) this week? In case you have not tried summer tires in snow, they are pretty useless; keep the car at home.
I would have liked the summer tires but I bought in November and I alway have bought winter tires mounted on separate wheels to keep safe. With this being a lease for me, I did not want to make that investment.