Put tiny clones directly into flowering with only 10 hours of light and 14 of darkness. And they will still take a long time to ripen, and they will stretch and stretch. You will need to use lots of lst to keep them short and wide, lots of pruning may also help. If my bagseed turns out really lanky sativa I'm probably only going to flower one clone at a time and weave it through a grate so I have a big rectangle of stems and little bud sites popping up from that. Then when the rectangle is all filled up I will cut the apical stem, smoke any little bud that's at the end of it, and then just cut the tops off the buds as they stretch before they hit the ceiling. Or if the canopy is not very dense with foliage I will weave the buds through the canopy horizontally to fill it with dense greens, and then just cross my fingers that I can grow it long enough to ripen without having more plant material than what my cabinet can hold.