I have just been looking at the idea of shimming, can someone tell me the best way to do it? and can it be done without it being obvious if someone else inspects the cuffs? Does the metal have to be moulded to fit the individual pair of cuffs?
While there is never a "one-size-fits-all" answer, something that I've found handy is stiff plastic, particularly aspirin bottles and clamshell packaging (that clear stuff that nobody but a four-year old can open). While it's not all that durable, the great thing about the clamshell stuff, in addition to being free, is that you can easily experiment with different shapes and configurations, since it's easy to cut with an Exacto knife. When you find something that works for you, then you can use it as a template to make one out of metal.