If you were starting your trip in Cincinnati (CVG) you could rent a car and drive to Dayton for your first leg, drop off the rental car, connect at CVG for your second leg, and then on the return simply get off the plane at Cincinnati and drive your own car back home.

People use this "hidden city" trick all the time in Cincinnati (Delta) and Charlotte (US Airways via Greensboro). If only the airlines had more rational fare structures in their hub cities, there'd be no need to do this, but that's life.