You could get seedling warmers, its a plug in pad you put under seedlings to keep them warm for germination.You could put them in your nestboxes under the straw, and since they never get over 75 degrees it wont burn the straw and cause a fire.
http://www.amazon.com/Hydrofarm-MT10006-19-1-2-Inch-Seedling/dp/B0001WV010
Theres a link, they sell them at all farm stores.
http://www.amazon.com/Hydrofarm-MT10006-19-1-2-Inch-Seedling/dp/B0001WV010
Theres a link, they sell them at all farm stores.