In Jorge Cervantes growers bible, I do believe I read that humidity and temperatures can influence sex of a plant.
I have so many books its hard to remember what came from where, but im 100% positive I have read these are influences.
These are only factors that like I said influence, not change. Like said above, theres no guarantee, no set way to FORCE a plant to be male or female, but I do feel as if you can control the environment (heat, humidity, etc.) to help/better the chances of a female. Given the variations of strains, and genetics, theres no way to guarantee females.
This is probably a terrible analogy, but im blown so what the hell. Theres no 100% guarentee you wont get in a car crash, but you can take measures to try and prevent them with such safety features as ABS brakes, AWD and so on. Theres no 100% way to guarentee you wont get a male plant, but you can take the time to control the humidity and heat to try and prevent them.
Sorry if this didnt make any sense. Hope i helped. Happy new years all.