Adding empty comb and keeping dead air space above the colony is not wise at this time of the year. Knock the hive down to one deep. then add what they need in the way of stores by fondant or dry sugar. This will help. http://www.pennapic.org/feedingsugar.html
Never have empty comb above thew cluster through winter. This is where the heat will collect yet the bees have no use of that area. Normally they will eat up through the stores and by late winter will benefit from the trapped heat in the upper half of the hive. With empty comb above the cluster, something that NEVER happens in a feral colony or by the bees making, you are giving them a death sentence many times.