Take a piece of 1/4 inch steel stock about 4 inches long and about 11/2 inches wide. radius all the edges slightly. Place one end of the steel stock on the rivet the other end on the table shimmed up to match the height of the rivet and use your flush snap in the rivet gun. Works great for riveting those rivets at the trailing edge of the control surfaces. To make a dimple in that location take the steel stock and drill a 3/32 hole near the edge on one end. Machine counter sink it. Place it in the tight spot and use the male dimple die and whack it with a hammer, makes a nice neat dimple.