1. I am not a mechanical engineer
2. The smart solution would be just to buy the correctly engineered clamps for your application, and to sell the ones you don't need if you change them later, then it won't cost you all that much.
That being said, if you really wanted to use the same clamps in both applications, I think a shim with 2mm wall thickness would not be a problem since they are just clamped in between.
What I would definitely do however is to machine them with a lip on top and bottom so that there is no risk of them slipping out of the clamps. That, and roughing up the surface on the inside so that they don't slip on the chrome sliders of the conventional forks. Doesn't have to be anything crazy, just not a smoothly machined finish.