Cassy, I really wish I could tell you exactly how it's done successfully, but I have never been able to pull it off. But, I can regurgitate what I've been told to do over the years.
First, leave at least 1/3 of the plant alone, this means the buds. Low light is supposed to help it revert, as is cutting down the rootball for a transplant (encouraging roots to grow will help stop it from continuing to flower). Put that low light on a 24/0 photoperiod, too. Feed it nitrogen, and alfalfa can help push more vegetative growth out of it.
Remember, this is me simply regurgitating what I've been told, not me talking about my actual experience. I did all those things (or so I thought?) and the plants all eventually just gave up the ghost on me. I think I may have harvested too much from them, but haven't been bothered so much by it that I've tried again, I just take cuttings and root those, instead.