i'm not familiar with how your hinge pocket is iside the door, but could you possibly replace one hinge bolt with a longer one that would allow some excess threads to protrude inside the door itself ? you could attach a turnbuckle to this as the upper point. then attach the lower point of the buckle[using cable as you thought of] to ??? at the bottom of the door and slightly pull as needed. can you see where the door is flexing ? i wonder if it's the jam area of the door where the hinge attaches, or possibly maybe the whole door mite be "curling" just a touch , causing the lower , inner edge to touch the rocker. i know what i want to say, just not sure i'm saying it as i want to. as the doors are glass, is it possible to "massage" the bottom a touch just for the clearance needed ? or would that allow for even more droop ? how thick is the door in that area ? i hate to suggest "paint surgery" because the car really looks killer !