you need to stress them out. underwater them. turn the lights off for three days. then turn them back on. it might take a couple of times. they will herm on you.
You just dug up a three year old thread to give advice three years late, FYI. Check the date of the last post on a thread to see if it's still relevant before posting.
Oh, any by the way, herming is NOT how to make female seeds, it's how to make more hermi seeds. Reversing a fully female plant that you found after stress testing to eliminate hermis is how you make female seeds, and you revese them using CS or a similar solution, not stressing.