qwert has the right idea lol, though you might have to use Canadian coins. I was thinking of shimming inside the mount where the pipe inserts, rather than elsewhere, but whatever gets your dishmount (and dish) plumb.
Did something like that on a c=band pole a few years ago, top of pipe was not exactly flush, and therefore not level, which was throwing off my ku-bird tracking. Took off dish/mount, and being too lazy to grind off the pipe with a grinder, glued a couple of US nickels on low spots on the top of the pipe, eh , checked with my level seven ways to Sunday, and put it back together. Works great.