I've done this many times and found it flawless..just cut clones off them, tag em'and pop them into a clone machine and set with 12-12, For me they'll show their gender in 7-10 days...and some show gender even before they show roots. Although I've never put cuttings in a glass of water with 12-12 lights I'd bet it would work. No need for a clone machine really. I'll try it this Spring just for the hell of it.
If you choose, let the clones root out fully and use them yourself or gift them out.
just as a side note...I've had great experiences with fem seeds...no herms or weird shit but note that I have only used HSO and Dinafem fem seeds. Some of the reading I've done stated that Dinafem does a lot of fem seed production of other breeders regular seeds. Dinafem is a good company IMO.