Bend your uppermost branches at 90 degrees until they crease and stay that way. I know it sounds counter intuitive, but they will mend themselves within a couple of days - I did not notice any decrease in growth rate when I did mine. I only did a couple on each plant every other day or so, since I was wary of trying it in the first place and didn't want to stress the plants too much at any one time. The good news is that mine quit gaining height (and continued to gain mass) at about a month into flowering, my last grow was only my second and I was afraid there was no way I was going to be able to finish it at the rate they were going, but everything ended up fine. I didn't look at your setup closely before responding (and can't see your pics now), but is it possible to drop your containers at all and gain space from the bottom?