There is one thing I just recently did and it seemed to help quite a bit. The collar has a front and back(or bottom and top). All collars have two sides, the one we see and the underside. On the JAL jackets (as well as most vintage coats) its leather on both sides. On X marts jacket it is felt on the back (same with the pockets) this makes it hang lighter and more freely. When you get a jacket new, they are glued to each other and that makes them more rigid. All vintage jackets that I own, the glue has worn off. I pulled them apart as well as I pulled the pocket flap apart and I made sure that all the way down the button area was freed up. This lets each piece of leather hang more loosely and in adds the desired "worn-in" wrinkles. Then just tug on it, twist it, roll it, stretch it etc and it will loosen up nicely.