Here is a possible easy and relatively inexpensive solution, but it depends on what the definition of "remote" is. Weighs 1.5 lbs and requires AC power. Will keep the battery fully charged and somewhat warmer than would otherwise be the case (but its not intended to heat the battery). Have used one for many years and recommend it highly.
http://www.power-products.com/Datash...P6001-1001.pdf
Here is another possible solution, but may not meet your "no apu" requirement, and not so inexpensive. I have seen these at HAI but have never used one:
StartStick - Aviation Battery Systems LLC