Flowering is a phytochrome response. Phytochrome exists in two forms which are converted between each other. One form (Pr) is converted by red light (around 660 nm) to the other form (Pfr) which can revert to Pr in the dark or by exposire to far red light (around 730 nm). Using the ratio of Pr to Pfr a plant is able to detect the length of the night and when it is shaded. The night length triggers the flowering response for most plants. Some plants like cannabis will flower regardless, but others have an absolute requirement. Furthermore, some plants (cannabis again) flower when the nights become too long, but others flower when the nights become too short. Once a plant has been indiced to flower it continues to do so due to a chemichal propogated from the leaves. A leaf from a flowering plant can be grafted onto one which has not begun to flower and that plant will subsequently be indiced to flower.

From this we can reason that yes, a long dark period (maybe 14-16 hrs daily or, I suppose, a 36 hr "shock treatment") can be used to induce flowering in cannabis. Alternatively, you can increase the amount of far red light your plant recieves such that it recieves more than the amount of red.