I would just ponytail train them for 6 hours per day to make them branch out. Then when low stress train them a bit. and maybe bonsai bend the mains stem. Identify a flexilble spot somewhere under the third or fourth to last node, soften it like u where to supercrop the plant, then wrap some steel or aluminium wire around the stem in a spiral, leave some space around, then gently bend the wire, plant will bend with it, easy.