Cut 4 Blanks of 1/2" MDF to roughly 240 mm x 770 mm. (9″×30″)
Open file and set blank on table reasonable square. Secure and carve, I did each blank individually so figure 15 min x4.
Drill out holes to 100% depth, counter sink 4 corner holes and one center hole.
Measure 30mm from the center of the holes running lengthwise, and 15mm from the center of the holes running widthwise and draw a rectangle. Cut the excess material off on the line to give you a final size of 220mm x 750mm.
Anchor the spoil boards in place and surface to spec. Mark the location of each board because you will have to spin the boards and move the outer two to get the entire surface. Once surfacing is complete return the boards to their original locations.