I took my boots to a local boot repair shop last week to see what they could do. They ended up making a sideways H pattern cut from 1/4" dense foam, then gluing it to the outside of the liner so the bars of the H go around each side of my ankle bones. Is the same idea as the J bars, but it's 1 piece and covers a bit more.
Also picked up a pair of Sole red orthotic footbeds, which raises the heal a little.
Haven't rode with them yet, but it's significantly better just standing and flexing my foot trying to life my heal. I can definitely feel the foam grab my ankle bones when my heel trys to lift.