Four inches from the center seemed to be the best place to put the zip tie. I clamped all four separators together, measured the holes the best that I could, started with a punch, drilled screws at each point to keep the separators together, and then pulled the screws one at a time to enlarge the hole.
I did not have a bit large enough for the zip caps, but there are larger ones at Mom's house. Also, my zip ties were too thin for Vekke's caps, I could not get them to work together, so instead of looping a zip tie around a wheel spoke, running it through the separator, and through a cap, I ran it through the cap, then the separator, and then around the spoke, which was difficult with a giant aluminum circle in the way.
The caps do not sit flush and I cannot close the caps until I find the right ties, but this is an improvement, right?
I plan on spraying them with black Plasti-dip.