Are your plants still in the vegetative cycle or have you started to flower yet?
Bro Grunt gave you perfect advice. You can tie a string to a weight of some kind that is about 5 pounds and GENTLY pull the top of the plant over just a few inches a day for several days. Each day, the plant will adjust to the strain and "relax" some. A plant can be pulled over in this manner, a remarkable distance. If you get the top pulled down a foot or so, it will make an "S" and head for the light again.
Height restrictions are something that experienced growers include into their plans for the timing of the grow cycles of MJ. As you've seen, not doing so will cause lots of problems later. You can fix this problem by following Bro Grunts advice.