How about snapping them over the edge of some 'Die Knife', like they
use to make cuts in cardboard boxes? It comes in long strips and is
sheared to length, then a thin router bit cuts a groove into plywood to
hold it. A rubber mallet is used to tap it into place. Ad an adjustable
backstop with a lip to keep the board level will help you align the
score on the sharp edge & snap it off without spreading all the stress
through the boards.
It's tough to do with components on both sides of the board, on both
sides of the score. There are tools to do this but they were too
cheap (but wasted *tons* in other areas). The problem is that the
recommended score and mouse bites are marginal, and of course everyone
crowds the edges (raises hand). "I *know* that ten pounds will fit in
that 5# bag."
I don't have any scraps left, but any company that makes the dies for
cutting cardboard boxes will have some. A lot of box companies do it in
house. Every plant I was ever in had the tools & supplies to make &
repair the dies.
I would think you'd need a different tool for each board. Several, in
fact. Once we got the recipe down, there weren't a lot of problems.
The problems were up-front, when the schedules are the tightest, of
course (get the thing to market so the boss can afford to pay us).