You've got it all wrong. Instead of shimming the clamp you need to dump your frame and buy one to fit that super trick seatpost clamp....
I have to go with the others that say a shimmed trick clamp ain't so trick when the shims are there. Stick your trick clamp into the parts box for some future project bike and get the correct size. Besides, unless you're very lucky and one or two layers is just the right amount the clamp won't hold with a full and even 360 grip. And when that doesn't happen you'll find that your post wiggles around and sinks down the tube requiring you to stop and lift it up into place frequently.