Empty the contents of the box. Be careful to leave the flaps intact.
Insert the paint stir stick into the empty box. Lay the stick flat and center it along one of the wide walls of the box. Secure the stick with tape.
Mark the outline of the stir stick against the box flap underneath it. Draw from the crease at the bottom of the box flap all the way to the top.
Cut out the U-shaped area bounded by the pencil marks. You should be left with two independent flaps on either side of the stir stick.
Pack the box with the packing peanuts or newspaper. Take care to pack full enough to give the box structure, but without causing it to bulge.
Fold in the box flaps. Begin with the smaller side flaps, then the cut flap around the stir stick, and, lastly, the remaining long side flap. Seal with tape.