Make a aluminum foil pan large enough to accept the piece of balsa you are trying to bend. Fill the pan with household ammonia, and let soak for however long to make the wood soft (maybe an hour or so). Form the wood over the formers, and allow the wood to dry. When the wood is dry, it will have taken the shape you wanted, and you may glue it in place. The ammonia will smell up the place, so allow ventilation.

Les