This would be easier to explain with the shotmaster but I'll give it a shot. Once the section is fully operational I'll create some layouts for clarity.
My recommendation to fine tune your screw shots is a little drill involving simple straight pots of the blue to either side but any straight pot setup can be used. I choose the blue because it allows the easiest setup and the distances involved are about the range you most commonly need good control on. This drill works equally well for stun-run through or follow shots.
You want a simple straight pot that allows for the cueball to draw back or run through on the same line as the object ball, 3 feet either way is optimal.
Parallel to the path of the cue/object ball I would stagger some "target" reds , perhaps 6 inches apart.
The idea is to pot the object ball and draw the cueball back or run through to a specific "target" red position. I've suggested 6 inches apart for the target reds as generally you'll be OK being within 6 inches of your desired position but you can reduce the distance between to further refine your control. If you want inch perfect control, put your "target" reds 1 inch apart.
Hopefully this is clear enough for you to get started but please let me know if there's something that's confusing and I'll do what I can to clarify.