i know this is older but if you still have them and are going to ship them ups store usually have boxes that are almost perfect to ship wheels.
just put wheel (without tire) inbox put a piece of cardboard on top of that wheel then set the second wheel in. you might have to cut the box down a bit but it should be close to the correct size.
I brought a tape gun with me and got the boxes then put them together then wheels in them right on the tailgate of my truck then carried in to ship. I shipped 4 wheels in two boxes cross country for a total of around 100.00.
