If ski manufacturers use center of boot as the "balance" point -- and this is true as you suggest. Then this WOULD NOT be ball of foot -- and indeed verifies in my mind that they mount the bindings back a few centimeters from what some consider the ideal location of the ball of the foot area as being the true 'balance' point.
I'm not sold on the whole 'ball of foot' idea as classically stated, not because I think it is wrong, but because it is over-complicating the issue, particularly when you consider the role of the arches of the foot, and how people vary.
-- Is trying to figure out where the ball of the foot is in the boot.
This is not going to be easy although the boot, properly sized to the foot will give some indication.
I don't bother finding the ball anymore or anything else that requires transfer of internal to external dimensions.
It is easy as pie to find the external balance point, if you size the dowel right. With a 3 inch dowel I reckon you can get to within 2mm.
Smaller than that and the action is too "fast" for the balancee to be precise with foot placement i.e. you're measuring teeny differences; much larger than that and the balancee starts getting nervous without poles or an external bar.
All IMO, of course, and I should say I've only done about 10-12 of these for myself and friends.
Even if the "balance" point is found, either dynamically or statically -- it's still an ideal that may not fit the way you've skied for years... even if its "right".
I think you'll find that, if you have found the balance point, and your boots allow you to flex in a full range of motion whilst at that balance point without levering against the skis, all the rest will adapt eventually.
One "existing technique" point that is not addressed in the article is taper angle and sidecut depth. On skis that do not have very large taper angle, or that have a small-radius sidecut, or both, moving the bindings forward will cause crossing of tails unless the skier is really careful with their stemming moves. This is how I kecked up my twintips and made them useless in bumps. They carved up a storm, tho.