I just heard back from TireRack support. I had asked the question as to if a centering ring was really necessary, since the wheel has tapered lug holes, and the lugs are tapered as well. He said that as long as there's no weight on the wheel when torquing the lugs down, it is fine to not have a ring on there. I was a little surprised to get that answer, but it also makes sense given the wheel and lugs.
In the meantime he is still looking into the issue with their technical support.
Please don't do that. The wheels (and the car) are designed to take vertical loads through the hub ring, not through the lug studs, which is what will happen if you don't use the centering ring.
Two methods that will work pretty good:
1. The sandpaper method above -- lightly sand the inside of the centering rings with 400 grit, then clean and lubricate -- they'll go on. The only problem with this method is getting an even and consistent sanding.
2. This is an old trick we used to use to put bearings on a motor shaft when we rebuilt electrical motors in the Navy. Heat your kitchen oven to about 200 degrees F. Once it's up to temperature, put the centering rings in there. Get two potholders that are large enough to fully cover the centering rings, and a 3rd potholder that you can hold onto. Put the first two potholders in the oven along with the centering rings. Leave the centering rings and the potholders in there for about an hour.
Get the car ready for the centering ring installation, wheel removed, up on the jackstand, and close to the house, preferably in the garage.
Do all of this in one shot because you need to do it quickly to avoid the centering ring cooling down before you can get it on the car: Quickly take the centering ring out of the oven and make a "sandwich" of the two potholders that were in the oven and a centering ring, i.e. potholder, centering ring, and potholder stacked together. Then use your 3rd potholder to take the entire sandwich out to the car. This is to prevent the centering ring from cooling down. Now in one quick move, take the centering ring out of the sandwich and put it directly over the hub all the way using leather gloves.
The heat of the oven causes the centering ring to expand, so it will fit. Be aware that as soon as the centering ring touches the hub of the car it will cool down and shrink, so you need to get it positioned correctly on the first shot. If you don't, it'll shrink and tighten in whatever potition you have it, and it'll be difficult to remove without damaging it.
