you were too early putting the second box on. now that there is brood in the top box you can either move the drawn frames from the second box down and put the undrawn frames in the upper box, or move the undrawn frames closer to the center of the bottom box. not too close to the center. the problem with all this is i don't know`your low temperatures, and whether there are enough bees to cover the brood when you start moving things around. i would also be feeding syrup if you are trying to get foundation drawn. you could also force them back into one box, that depends on how active they are in the second box. i'd probably just cycle the empties toward the middle as thats the least obtrusive option.