I guess I just have round holes for the screws in upholstery plywood, otherwise you indeed need to equalize the levels so that the pull handle rosette fits the upholstery material. I do not know what was the original solution...
Anyway, if I were to fabricate them, I would use aluminum bar, say 3mm, not wood. I would drill 5-6mm holes, then cut the length to get the rectangular shape. Probably 10min of work each if you have a vice, drill and a simple metal saw.