actually there are acouple ways of making female seeds. the gibberellic acid way, hermied seeds(which are more likely to be female than male but have a better chances of being hermies themselves) and some new way GreenHouse Seeds is advertising...not sure if the GH is credible though.

my last bagseed plant was from a hermie seed.(messed up the first grow), most of the seeds were female, but in the end.....they still sprung up nut sacks.