One thing I have tried with some success is spreading the unscented hunting deodorant on my feet just before I put on my liner socks. My feet have never sweat all that bad, but the deodorant really cuts down on the amount of moisture in my boots and thus helps keep my feet warmer.

Another thing I learned from watching a show on the Discovery Channel about the science of cold, is that you need to make sure you are keeping your core as warm as possible. If your vital organs are warm your extremites will stay warm. Last season I tried one of those sticky heatpacks on my lower back and I felt great. It actually helped keep my back feel better throughout a long sit in the treestand. I try to spend as much time planning how to be comfortable as I do planning how to be scent free. Both are critical to enjoying hunting.