I don't frown, I just do it.
My Holdsworth has a 26.4 Cinelli stem mated with a 26.0 later Cinelli bar. I added brass shim stock until the two clamped up tight. It hasn't shifted since, but it did take a little trial-and-error until I got just the right amount of shim (the stuff I use is .01 mm thick)...you can do the same thing with aluminum can stock.
As we all learned from "Zen and the Art of Motorcycle Maintenance" this is perfectly good, even for a BMW.