There are a handful of companies that will gender test a clipped piece of a leaf. You'll need to pop the seeds and wait for the plants to get big enough true leaves so you don't affect growth by snipping part of a leaf for a sample. When I've done it, I usually wait until the seedling is about 2 weeks above soil (for photo plants). They're not inexpensive though. They generally range between $10-$15 per test, unless you can catch them on sale.
These companies exist for people who live in areas where people can only legally grow a few plants at once for medical purposes--and need a continuous supply of their meds without worrying about whether the cops will kick down their door and find that they're 2 plants over their legal count. Knowing which plants are female could save weeks worth of time & resources and don't restrict people to growing only stuff that's been made into a fem seed. Sure there are ways of manipulating plants into showing gender sooner if you have the time & space to do that.