What type of pedals do you use. There a few ways that I can think of to create a 2cm spacer to put between the cleat and sole of your shoes but you may just want to have a spacer fabricated by a cobbler, machinist, plastic fabricator, friend, you, etc. to just use whenever you buy a new pair of shoes it can just be transferred over. If it were me I would just buy a 2cm thick block of nylon or aluminum and shape a spacer with the two or three hole bolt pattern to fit between the sole and cleat. You might want to try stacking some metal washers on the mounting bolts between the cleat and sole and experiment with different heights first. I don't like the idea of inserts as this can create shoe fitting and comfort problems. You may also want to post in the Adaptive Cycling: section as there may be businesses that already do this sort of thing.