Alright, progress has been made. The first prototypes have rolled off the line.
The adapters are milled out of billet T6061-T1 aluminum, and currently is not finished. The plan is ultimately to have them anodized black, but for now, it's easier to test them without any paint. They are designed to work exclusively with the BMW TE37SL Bore of 72.6mm (this is the Volk measurement, not BMW), but can be changed to fit any other TE37SL bore.
They've been designed to accept the GT style Volk centre cap but it should fit any of the o-ring Volk centre caps.
I'm going to be away the next few days on business, but over the weekend, I plan to do some testing (e.g. hard braking, highway cruising) to make sure these things don't just pop off. I'll be the first to say this though, these should not be left on when tracking your car. I'll take more pictures over the weekend with the adapters and caps on the car.
PS. Sorry about the picture quality, I was using my iPhone.