One approach that might be tried out, with the Dremel or similar variable speed motor, is to use the Dremel Plunging Router, mounted onto a heavy Lexan sheet that is adjustable with legs that can be replaced in increments of one half inches (1.5") wooden dowel x4 @ length.
A fine blade in a chop saw will give repeatable lengths for each set's length.
, IMO.
Secure each screw head beneath the router-table and just by plunging, ensure the drill or mill is centered properly, and the plunge length is set to just the top of the screw head's top, before plugging the power cord in.
IMO, the camera can be held secured enough in a small milling vice or, don't laugh, a supporting surface for the camera of Legos, mounted on a second level board, with nesting pipes, used to connect to the Dremel Board's legs into one unit.
Power up and over the problem screw, secured flat, begin to dip the router into the screw head, in very small increments until you've reached your goal depth.
Reset up the camera, new screw placement, router height, etc and repeat.
You don't need a lot of downward force to keep the drill or mill moving into the screw's head or below. Just let the Dremel type tool, do the work, keep it steady and again make your depth.
I think this is easier than said, and should give repeatable results.
IMO