just let it grow naturally....the plant will bud on it's own at the end of the summer. but you could do what you just suggested...artificially put the plant on 12/12, cause i know you don't want it to grow very tall.

however, if you let it grow naturally outdoors, you could always trellis the plant so it grows horizontally and stays short.

if you are going to artificially put it under 12/12, don't use a burlap sack. it will damage your plant cause of it's heaviness, and once the plant starts budding you definitely don't want anything wrecking the buds. i had to cover my budding plants with plastic bags to move them one time, and the buds got slightly damaged. you gotta be really careful with them delicate babies./