Pin the tip of the plant down and grow it in a circle round the pot seems to be the main lst route, tying the branches down will stop it from futher getting taller. Just do it once and you'll know for sure, i am definatly the wrong person to ask about lst but from your situation with the book shelf i would also suggest autoflowering varieties as these will finish very small and compact and give you that extra yeild you talked about. If the stem is strong and the growth fast top and put straight into flower if you really want. You need some hands on practical experience now so go for it and stop asking!lol P.s. if you grow autoflowers you need to make sure you are good because they will not wait for your mistakes in growing. From the sounds of your plants you will not have any problems here. Experiment with the knowledge you have, now go do it! Good luck