One trick is to drill a small hole at the very tip of the crack at the point where it where it meets good material to increase the size of the area subject to stress which should keep it from spreading further......the larger the hole, the greater the stress relieving area you create, but don't overdo it an 1/8" should be fine and then duct tape the crack and hole you drilled.... a large washer as will fit under the screw head would help to further relieve stress on the damaged area.