Placing a block so and closing the door onto it should push that part of the door outwards relative to the wing. The original recommendation was to use a 3" length of 1" square metal bar. But if it is going to be that thick the length is immaterial as the door will be about half open. The width should be as much as possible to fit into the hinge so as to spread the load, and if you use a block of wood as here it will also cause less damage to paint.