Cut the board along the diagonal. Use a hobby knife and a metal ruler or other straight-edge guide to cut out copper to make a trace along the long edge of each piece. Orient the cuts to mirror each other. Then also cut two 1/4" by 3/8" copper-clad rectangles for spacers between the two blades.
TRICKS FOR CUTTING THE GROOVES: Xacto-type blade will break off at the tip while cutting the copper because you have to press down pretty hard, but that's fine. Keep using the blade even after the tip breaks off. When it dulls, just break more off the tip with a needle-nose pliers (WEAR EYE PROTECTION) to get back to a sharp edge. Sometimes I snap off the blade tip before I even start so there are no surprises while cutting. You can save old blades for this because most get dull only near the tip. To get a clean open groove in the copper, cut once to get a line, then cut a a few times with the blade angled to one side, then a few more with the blade angled the other way. The angles make a clean beveled edge on the copper.