Do you have a flat ceiling with a truss-style attic above? Dumping a load of moist warm air into your attic space might cause troubles unless the attic is very well ventilated. Safer to duct all the way out to the gable ends or to the soffit.
What about poking a hole through the wall to the outside? Install a dryer vent or something similar on the exterior wall. As long as the work is executed professionally, caulked, and painted, it's unlikely anybody would question it. Unless of course you grow some smelly weed and your "dryer vent" is pumping out air that isn't Downy-fresh...