Well the “knee drive” thing was common in race coaching even 20 years ago. They used to have people hold the inside knee and drive it in.
Yup, and we still do. A few variations -
First sensory feedback, hands on kneecaps, feel knee position through the turn: are they both tipping at the same time, and to equal angles? Or is the inside knee starting to tip later, and not as far as the outside knee?
Then some active movement/focus such as,
a) Hands on kneecaps, now use your hand to tip the inside knee in the direction of the new turn early and far
b) As (a) but with hands on the insides of both knees. I don't like this one as it can backfire if the skier pushes knee against hand rather than hand against knee. But some like coaching this.
c) Hands outside both knees, near but not touching, focus is to try to drive the inside knee to touch the inside hand early in the turn. My favorite among these.
etc.
Also appropriate for recreational instruction, except in my opinion (b) which I don't like for racers either. But some do.
Of course it needs demo, skier reflection, feedback, and to sit within a broader instructional goal. And to be sure that all the focus on tipping the inside ski doesn't end up in overweighting the inside ski.
You can also fuss with therabands around the knees, but that takes some adjustment to be sure it isn't too tight which would force an A-frame. If too loose it ends up tangled around the feet. Lots of laughing and time passing. The ideal size also varies with turn dynamics. But (an hour later...) if you do get it adjusted well for each skier, it can provide a good sensory cue to actively drive the inside knee into the turn.