Hope the research is going well!
Well, this B player will give it a shot! lol
Actually, the "system" I use entirely hinges on using the cue as a staight edge to help judge the cuts.
If the balls are really close and the cut is thin, (holding the cue over the table) I'll sometimes line up the edge of my cue with the inside edge of the cue ball and outside edge of the object ball and using an imaginary right angle, I try to see how far from 90 degrees the cut is.
One key thing to know when calculating angles for me is that 5 degrees is exactly the width of a 2 1/4" ball from just over two diamonds away (only 3/4" over) on a nine foot table.
I try to regularly practice thin cuts at 5 degree intervals and when it get's to game time, I'll judge thin cuts as super thin, 5, 5 strong, shy 10, 10, 10 strong etc. For whatever reason, it seems easier for me to visualize these shots as something less than 90 degrees rather than some big number like 75 or 82.
As the cuts get heavier, I'll sometimes hold the butt edge of the cue over the contact points and see where the cue is pointing. With a little adjusting, sometimes mental, sometimes physical, for the distance between the contact points and the center of the cueball, I'll sight down the cue and pick a spot on the rail, or maybe somewhere in the room where I need to aim the center of the cueball. I use this mainly to help tell me where I should stand before stepping into the shot. (Usually, when I step into the shot right, I'm okay from there.)
I guess if using your cue as a ruler to help figure out the lines qualifies as a system then a system it is. (As long as you don't lay the cue down on the table and let it go right?)
Again, good luck with the search. I'm interested in where this might go!