It isn't necessary to manipulate the photoperiod of tomatoes to either induce flowering or, to take cuttings. Tomatoes are among the easiest plants to "clone". Several methods exist but personally I take a cutting from a plant and simply place it in a glass of plain tap water and put it in a window sill or on the back deck. Within 7-10 days new roots will appear and it should be ready for transplanting to soil. Tomatoes that are "indeterminate vines", naturally grow more or less in a sprawling, horizontal pattern and are very easy as well. As the vines grow outward, soil can be mounded up anywhere it touches the ground. Once roots have been put down by the vines in these locations you can simply detach it from the mother-plant and relocate to any sunny spot. Tomatoes grown later in the season are generally superior in flavor to early varieties so this makes cloning ideal for late starting clones.