Thanks for the suggestion. I did read your other post, but have not yet had a chance to comment. I found your approach interesting from several perspectives, but I do not think it solves my problem.
My current approach to T'ai Chi is from external to internal, so that I do not practice anything internally that I cannot feel physically. I have found that when I attempt to proceed from internal to external, I often cannot make my visualization practical or effective. I have also found with this approach that what I think I am doing externally is actually woefully insufficient. I also find that I end up improperly training my intention (or "yi") and so do not have the proper feel for the power, shape, and limits of the technique.
A non-T'ai Chi example would be a golf slice. To correct a consistent 30-degree slice to the left, one could aim 30 degrees to the right. Ultimately, though, one's golf stroke would not improve, because such a strategy would mean never getting the proper feel for how different wrist angles affect the flight of the ball.
Your visualization might help for waist turns I already understand, but unfortunately does not help me create something where I have no physical understanding. Thanks for the suggestion, however.
By the way, is the change in mental ball spin, the only "waist movement" you make in the posture transitions I mentioned?