Going to try this during my next practice session
I think you're right on this. Lewit also wrote a book called the Secret of Spanish Tennis. One chapter is titled "Suffering" by the way. I made the mistake of giving it to the pro I regularly work with after I read it. He ended up killing me with hand feeds shortly after for months. It's brutal drilling especially for a 40+ man like me. I can't recall exactly, but I think the double bounce serve feed I mentioned above may have come from the book or one of Lewis' videos. Back to the hand feeding, I highly recommend it for the guys who struggle with pushers and junk ballers.I don't really recall when I first came across this type of feeding.
Have been working with another coach, a former D2 player, on his serves & returns. I had asked them when he first saw this type of feed. He had indicated that he recalls seeing it about the same time that he was learning about the Spanish method of teaching.
Not sure if this is part of that system since the Spanish system employs quite a lot of hand-feeding drills. I first learned of the Spanish system around 2011.