If its jus 2 pax and no elderly or infant -bus tour is fleasible. As per stated, limited timing plus very time consuming and not so cheap. (2 pax is still ok). No worth the cost and time of in group of 4-5.
Can plan to stay in Naha 2-3days and go stay northen in Nago 2-3 days and schedule bus back to naha airport. Can be done but extensive reseach and planning needed.