I've experience this in a different boat. I replaced my entire compression
post with starting from the top of the keel in the bilge with a solid block of teak
, then a solid 2x8 piece of teak
spanning two floors, then a stainless 4x4 square tube to under the cabin
top. What I imagine you would want to do is just part of what I did by cutting out the bottom 2" plus and adding a solid block of teak or non-compressable plastic, or non-corrosive metal, held in place by shoring or fiberglass
I used a hydraulic bottle jack to get clearance enough to install the compression post. Don't over do the jacking.
Good luck in your repair.