However, it's actually a rather trivial operation to shim up the stationary burr to shift the grind in a finer direction.
Don't get me wrong. If you've got a great espresso machine, don't skimp here: get a Jolly or a Rocky or something like that. But if you were considering a Gaggia, a Baratza, or other low-end espresso grinder, give this a whirl: once modified, it easily compares with that class of grinder.
Step 1: Remove the stationary burr.
Step 2: Cut the shims.
You'll probably need between two and ten shims, depending on your machine. The Supreme Grind isn't as precision-manufactured as some, so your finest grind will be somewhat finer or coarser than that of other machines: you may need more or fewer shims than I did.
Step 3: Fit the shims to the machine.
Be sure to both tighten the burr completely (though be very careful not to strip the screw-post threads), and ensure that the shims are not wrinkled or positioned in any way that could cause vertical misalignment of the burrs.