curious of prunning a rubber plant for bulky growth instead of vertical height
It will stunt the growth of the plant to do this in any way, but you can "top" the plant or bend it down. Topping the plant is cutting the top node of the plant's new growth to let the lower growth grow bigger instead. Bending the plant merely allows the lower branches a chance to get more light and grow faster, usually using twine or light string. Either way will cause a pause in the growth of the plant, but topping the plant will stunt it more than bending.
You have to be careful to also cut the stem at the right place. Especially with rubber plants as it will destroy several inches downwards.