I had this problem on my Trek 610, but the fitting error was much less - a 27.2 was too small, but a 27.4 was much too big. I shimmed it. I bought an assortment of brass shim at the local hardware store, and tried several thicknesses. The one that worked was (don't recall exactly) either .004 inch thickness or .006 inch thickness. It took several tries to get a shape and size that worked, and to learn how to install it (greased, all surfaces) so that the friction did not destroy the shim or bunch it. After a few installs it has a crease, but it's not a big problem.

f your discrepancy in size is "just a gnat's ass," a 1 or 2 mm shim will probably be much too thick.