Wait until your ready to harvest the plant, but chop the main stem an inch above the lowest branches, leaving a short stalk with 2 branches sticking out (remove any bud from these branches, but not leaves (if there are any left).
Put this back under veg lights and wait. The leaves will die off naturally, but with a bit of luck, in a few days you will see some fresh growth appearing at the branch nodes, and the plant will start a new veg cycle. In a few weeks, you should have a few shoots that can be used to make clones.
I discovered this method when some of my plants were stolen years ago. I had made a temporary greenhouse against the back wall of my house from some plastic sheeting and bamboo poles. Somebody sneaked in one night and cut all the plants (20), leaving just the pots with stalks sticking up. I was so upset, that I just left the pots alone and concentrated on my indoor babies.
When I finally went to dismantle the greenhouse, some of the stalks had developed new bushy growth around their nodes, and they went on to grow and flower successfully indoors