On big differences that need to be shimmed, I agree. However, for 25.4 to 26.0 a can shim is the way to go. You can't get a better setup for it than that.

What I do for a can shim is drink a beer (it must be beer, or else it won't work right on your fixed bike), cut the thing open with scissors, lay the sheet of aluminum out flat, and cut the right width strip out with a straightedge and utility knife. Cut it to length, apply to bars, install in stem. Easy, effective, safe.

Oh, also, you can buy self-adhesive aluminum tape that I believe is used for ductwork. It also works really well for shimming bars, though it *will* leave some residue if you ever take it off, which really doesn't matter anyway.