I'd score one side at least with a box cutter where you want it to crack. & then use the vice jaws, or make up a jig with a slot in it to snap them off with.

What I have noticed is that most fingerboards seem to have a row or two of 'thru hole plating' holes about 2 or 3mm away from the edge of the gold fingers, the holes seem to have a gold plating right thru it.
I'm thinking that it would be good to break the board thru the holes & that would expose the 'thru hole plating', so the gold inside them can fall off when they are acid washed.