If you have a saw table saw would be the best way and a plywood blade with lots of teeth. You'll still get a crappy cut line, jagged somewhat but it'll be cut, or you could score it like glass, place a straight edge on the line and run a sharp blade (box cutter) over it several time, move over to the edge of the table, line the score up near the edge and push the free edge down in a sharp quick motion, if you scored it enough it should break clean just touch up with sand paper
hth