I bit the bullet and bought bought 2 new tires for the rear.
Stupid Tire Rack wouldn't let me order just 2 tires online without entering car info, so I had to call.

Guy on phone kept explaining these are "summer tires and directional", we need the car.
He finally placed the order when I explained this size wasn't stock on the car.

And yes, I did try to find another car that uses 275/40/18 to enter online before calling....