Your best bet is to use a different style of copper hanger. There are a few types, depending on whether or not you have a flat fascia, or molding. You screw a bracket to what you have, bolt a shank to that bracket, and then bolt a half-round hanger to the shank. They are adjustable and work well. The under-slate hangers are a pain, and you do have to replace slate to put new ones in.