Yeah, I thought about the problem of doing a larger thing like that awhile back, and saw the same problem. One thing that did come to mind was using a high vacuum to compress them together, so all you’d need is a flexible, sealable envelope like vinyl, and a pump. But of course that is a max of 14.7 psi of pressure. Sounds much less than the impact from a hammer on a stamp.
But it might work just fine, or not. The extra time left sitting there may deepen the impression with wet leather, but probably not for dry.