What exercises can lengthen spine?

Not really. However, many exercise techniques have been proven to make bones stronger, but not really larger. Lying down all day and not moving would allow the cartilage to expand (as it does overnight) but only very slightly and you would only gain around 1cm or so overall and the effects would be temporary as the cartilage would compact over the time you spend standing up (as it does during most days). By releasing and relaxing the muscles that are associated with the spine the same thing can happen, you can be taller. There is a physiological law called Wolff's Law that states: " that every change in form and function of a bone, or in its function alone, is followed by certain definite changes in its internal architecture and equally definite secondary alteration in its mathematical laws."