In the above shot we, can see that the OP skiers lower leg isn't flexed very far forward at the ankle---This is an upright boot (12 degrees). This along with the thin calf (his words) causes the skier to stand even more upright in the lower leg and on his heels in the "g" loaded portion of the turn which has his mass behind boot sole center---this in turn causes him to sink at the waist with his hips behind his heels.
I believe he will ski more balanced fore/aft with more forward lean provided in the boot. The reason he can't pull his knees forward during this part of the turn is that the dorsi flexors (anterior compartment muscles) are not among the stronger muscle groups in the lower leg. After all these muscles are only intended to clear the fore foot during swing through when walking, we don't go around lifting things with our fore foot as a daily exercise.
Boot alignment will affect the way a skier stands/balances etc...BUT...its an "adjustment"...like seasoning on a steak. Its not the steak. This guy is WAY out....its not a case of needing a few degrees here or there in the boots. His technque is fundamentally flawed. You can put this guy in the best fitted/alinged boots possible, without major technique changes he will still be sitting back.
Put the money and effort in where you will get the most bang for the buck....for this skier, at this stage...its not boot fitting.