Place the Plywood on Top of the Table
The auxiliary drum sanding table makes it easier to sand the full edge of a work piece. Because the sanding drum can't touch the drill-press table, if you ran the work piece across it, part of the edge wouldn't be sanded. But once the sanding table is in place, you can sand the entire edge.
Measure the drill-press table. Cut a piece of plywood to the table's exact dimensions. Place the plywood on top of the drill-press table, lining it up with the table's edges.