I had a VW based CMC/FiberFab kit. Bil collins now owns it (Angelica).The engine cover was probably the same as the ones with the fake tire bump. There was bump for the spare tire molded in to the cover. Depending on the year of manufacture, I think the engine covers were design with a fake bump when the VW’s had the “wide 5” bolt pattern. I think the covers are slightly different for a 4 lug IRS VW wheel.
I had IRS 4 lugs wheels. I used a stock VW wheel as a template and made a circular plate out of 3/8″ thick aluminum. It looked like the letter “O” with a hole in the center the same size as the center hole of the VW wheel.
I then drilled 4 holes, in the 4 lug bolt pattern, in the plate. I tapped 2 of these holes with the correct threads for the VW lug bolts. I used the other two holes to attach the aluminum plate to the underside of the engine cover using two socket head cap screws (allen head) that would act as locating pins for the two wheel holes that were not using the VW lug bolts.
The spare came off by removing the VW lug bolts and the plate stayed on the engine cover.
You could probably make a steel plate out of an old VW brake drum the same way and not have to tap any threads. A decent machine shop could probably cut the drum down to size for a reasonable price.