Its possible to do it, i kept my lemon skunk vegging for about 5 months, it was my first grow and i didn't know about 12/12, infact for the first couple of weeks i didn't even have a light, i got a CD and attached it to a plant pot in hope the small seedling i had at the time would burst into a bud covered plant from the CDs reflection..........that didn't happen. I Eventually got reading and a light and had it vegging for roughly 5 months. Altho it was Just a 200w CFL which is quite weak which may have been the reason i was able to keep it so long. But i reckon you should give it a go and am sure a few months down the line you'll have a good smoke.
Peace