I don't know if we are talking about the same urethane wheels but the one commonly used is McMaster 2477k36 (seen on 1114, 973, 2056 and 254 at champs amongst many other teams). We used them on a suggestion from 973's Adam Heard and found them to be great.
So that McMaster number in 60A is what we and they used.
http://www.mcmaster.com/#catalog/119/1117/=o1d4kk
The hub really is the easiest way IMO. You only need a lathe.
We machined said hub to interface with 1/2" keyed shaft. The hub was just a piece of 6061 round stock turned to press fit into the wheels bore. I took a look at 1114s hubs and they knurled them to make the press fit better. We didn't have the resources to do so but were fine through all of champs.
