I think this is part of it, but not all of what Bob means. He means to move with the skis. That means that the body stays over the ski and travels along the path of the ski -- not exactly, as the feet will travel a longer distance than the body, but it DOES MEAN that the skis are not being pushed away from the path of the body.
Personally, this has been probably the biggest issue in my own skiing and I see it in the vast majority of skiers, including level 3 certified skiers. One of the differentiating factors between those who can truly manipulate the ski to take them where they want to go is their ability to keep the connection to the skis so that the snow is traveling along the length of the ski rather than across the width of the ski. Given how few people I see can actually ski this way, and given how long it has taken me to start to get this element of ski performance, I don't think it is an easy thing to learn or master.
So, in response to the original question, how do you get folk to achieve this? I'll relate what my own experience was.
- It started with outside ski drills. Skiing tons of terrain to work on the relationship between the CoM and BoS. You are most likely pushing the ski around if you are on the inside ski. So, start with getting pressure to the outside ski.
- It continued with learning to drive the turn with the inside ski. Not that it has (much) pressure on it, but the inside ski/femur can "pull" the turn. JF Beaulieu calls the inside ski the decider, while the outside ski is the rider. It's the external femur rotation of the inside leg coupled with its shortening (pulling out and up) that gets turn shaped.
- Next was angulation. You've got to learn how to continue to direct pressure to the outside ski through body alignment. This means that the upper body has to remain over the ski, not dive in. You want to create edge by tipping the ankles and lower leg, not by tipping the upper body in.
- For that tipping move, you need to really work on tipping the lower leg. For this, I worked a lot on very short skis (136cm) that we use in teaching beginner lessons. Start with skating and learning how to create a platform against which you can push. That means you've got to learn to tip the lower leg first. Next, take it into J turns. Really focus on getting the outside knee to go in and down. Once you've got that, you can bring the inside leg back into the fold.
This is what I've been working on for over 5 years. It's not a simple process and I'm only now starting to put it all together.
Mike