I played around with this, but the shim sizes don't go below 2.50mm, and all of the shims in mine are in the 2.2x to 2.3x range. If you select one above the smallest size in the pull down, it will let you enter your own size, but when you click somewhere else, it overrides it with 2.50mm.
I'm guessing my shim sizes are typical, so I don't see how this will work for the C14.