I think I may be able to help on this one, the addition of gibberellic acid and kinetin should be able to force some of the leaf's cells to differenciate into actual growth tips. The application may need to be very precise with the use of soaked gauze wraped around the stem in order to force it to penetrate the cells but it should be posable. These hormones are commonly used in plant tissue culture for helping the plant grow out of a callus, the callus often being taken from leaf material. I have both hormones so I will try this out and get back to you guys... oh and they are cheap chemicals so maybe I can figure out the recipe for everyone else.