Stormy learning to bite where it is ok - early ball

Storm on box

Goal is to get the bite out and play tug and let him win, play tug for fun, satisfying hunt and bite needs, not needing food, and get the bite out where it is ok - and not at times when it is not ok. Storm saw Skye go for a ball, and occasionally went for it too at the time, months ago - Since he won't bite anything else other than real food, I got a tennis ball to rekindle a memory and it worked - it is the ONLY toy he will open his mouth for and I am using it as an entry point.
This is what one way of our "get the ball" looks like after a couple of days.