stilsons have worked for me on stiff posts , and the other thing that works is using plusgas not wd40 along with tapping outside of seat tube with a solid piece of wood to help release post
cheaper than a frameYou may have to sacrifice the seat post.
With a carbon post and frame? Agreed it won't damage it, but I don't think it will do anything else.Boil the kettle and pour hot water onto the frame, not the stem. Quickly twist and pull the stem before the heat transfers. If first time it does not work, allow everything to cool down fully then try again. This won't damage the frame or stem.