If you get non-feminized, grow them until you can get a few good cuttings off each plant, root the cuttings, as soon as they root, put them in a different area with 12 on / 12 off lighting. Make sure the dark period is really dark.

They'll show their gender and die, but if you labeled which plant each cutting came from, you can cull males before they get a chance to release massive amounts of pollen.