well a lung press, to me, would be where you either use your fist of working hand to press into the ball of the foot, whilst dorsal aspect is being supported by other hand. this helps to spread the metatarsals and so, spread the lungs, if you like.
OR, i'd put my palms on the plantar aspect, solar plexus to solar plexus and push, getting them to breath in deeply, releasing as they breath out.