I have one small inlaid 21 (clip removed) & wanted the same type of look on the leather pouch you're describing, but don't have the patience to wait....
So, I took the knife, stuck it in the pouch, and put the whole thing into a bag used to vacuum seal food. I left it there for 2 days in the vacuum sealed bag & upon removal the sheath was perfectly formed to the knife. It lost some of its form over the next few days, but still looks great.