If you want to make it a project, take a 12 TPI saw blade, clamp it between
a couple of pieces of angle stock, and scrape the surface sideways. :-)

Take two pieces of said sawblade, and use them in the jointer/planer
head? Make sure you align the teeth (though if one points left and
one right you might get squarish grooves?). Maybe go up a size or
three, 8tpi, 6tpi, 4?
--Glenn Lyford