I wonder if I could have drilled a hole through a 2x4 and clamped it
over the plywood to stop the rip? Would I have to do that on the drill
press?


Or you could lay down a strip of masking tape, mark the holes on that,
then drill. Or you could make a jig stick with the holes prespaced
and do that. Or get a strip of 'peg board' that has the holes
prespaced every 2".