I always overdo stuff, so this is how I would handle this. I would measure the width of the hanger. Cut a piece of wood thick enough to take up the space plus 1/8" Make it about a 1/2" wider than the width of the hanger and remove about 1/8" where the hanger is. Then just screw the hanger to the side of the door away from the frame with screws about 1/2" to 3/4" longer than the thickness of the block. The edges of hollow doors usually have a strip of solid wood around the edges, so don't go too far from the edge with the screws. hope this helps.