Well, I guess another method you could use would be to make sure you do everything at the right time, and have some place that is totally and completely dark to put them for 12 hours a day. I mean, If you already knew all this why did you ask the question? no offence meant, Just curious. Basically what you need to do is find a way to keep them in total darkness for 12 hours of the day, and hopefully in sunlight for the other 12 hours. I don't know how big your pots are, when I think outdoors in pots, i usually think a cubic yard of soil minimum cuz I don't move mine around, but since you are gonna force flower at this size, you don't need as much root space, you might be able to keep them small and moveable. It will give you substantially less yeild, though. You could potentially get like four times as much, but if you don't care about that, its your descision. I just wanted to make sure you knew what you are potentially missing out on.
What size pots are they in right now? That makes the difference wether you can easily move them or not, which will mean you have different options when it comes to this. If you are at about 1 and a half feet, and force flowered right now, you will need a minimum 3 gallon pot. It's a good general rule for most growers to have one gallon of soil for every foot of plant height (Yes, Fdd, I've seen the picture of your 6 month veg in the tiny pot, but most people can't do what you can do!). Anyway many plants will completely double in size during the flowering period, so you want to make sure you have a big enough pot and won't need to transplant, but something not too big that you can still move around easily multiple times a day. Your plants may be 3 feet tall or more when finished, depending on the strain. Do you know what strain you are growing?