On some video, several years ago, a worker sat at what appeared to be one of those double-board, steam ironing boards used by laundries for pressing clothes. I'm sure this was purpose built. The worker first steamed the leaf, quickly flattened it, then brought the two boards together---sssssss! Flat leaf.
Also, the way that wrapper is handled in Indonesia and other areas throughout its curing and packing is focused on maintaining a flat leaf. Don's Besuki is mostly flat. The San Andres is mostly rumpled.
Knucks found that if he performed the final stem drying by stacking leaf onto seedling heat mats, it came out flat.
Bob