I know its been over a month now since ur post, but if u have this problem next time try a product called Rock Juice.. Its a blooming product that is used in weeks 3-6, and wat it does is stop the plant growing upwards and re-routes all the nutes to the bud sites. It gives u real tight weighty buds. In ur case it would help as if u give it a little bit wen they have reached the desired height, then they will stop growing up and ur stems will start thickening to wat resembles hard wood. Also u wont get the massive height kick that comes when you start to flower them..
Hope this helps u for next time or any1 else who has a similair problem.