1) Supporting the thing with your jaw and shoulder so your scroll hand is free to move back and forth. (This is why the right setup is so important.) Seeing a video of changes in chinrest pressure while shifting helped me realize that you are supposed to hold onto the damned thing with your head sometimes and not just mildly stabilize it. While it’s not good to clamp down as if your life depends on it, you do have to hold onto it from time to time.
2) Using my arm muscles and not my wrist to vibrate has made a huge difference. The wrist is loose, but the vibration is coming from the arm muscles.
3) Using the pad of my fingertip and not the tip has also made a huge difference, because it seems to increase the “stickiness” needed to made my first knuckle rock back and forth when I move my arm, instead of having my fingertip lift up and down or slide back and forth over the string.
It’s really nice to be able to make a warmer, move “living” sound with the thing. I think I still need to move the shoulder rest around some though, just to get it more optimized.
And honestly, I’m not using it in music at this point. I’m just sort of getting used to doing it and need to do it with scales and things before anything else, to get used to it with all my fingers and on all the strings. Shifting will add another layer of complexity to this as well.
In other words, this is the advice of a rank beginner at this. It’s worth what you paid for it.
And I will ultimately need to get used to doing it with my pinky, too. Right now, I can only slowly manage it with index, middle, and ring fingers.