Screw trimming jig plate (for lack of better words)

[Moby Duck]

You might be able to adapt a reloaders case "chamfering" tool for this. The one direct from Lee Precision costs USD3.98 and doesn't give sizes but most from other manufacturers say from 0.17 to 0.45 inch. They are supposedly precision machined and ground and are hardened steel and most have a 45 degree angle. There are others besides Lee that make them in different styles but they cost considerably more than Lee. All are designed for brass of course, but for $3.98 I suspect that you will get reasonable service out of them for small steel screws. Shouldn't be too hard to make a holder to spin one of these in a Dremel, a lathe or a drill chuck. (Or just use your fingers).
http://leeprecision.com/chamfer-tool.html