The Jeep factory option block heater is in the freeze plug location. I never saw one leaking, (they are made of brass and copper) but I saw alot of the factory steel plugs leaking. He probably didn't want to do it because it's a pain in the arse to install one! If I were to install one, removing the intake/exhaust manifold would make it quite easy to install it properly. If you don't get it squared up in the freeze plug bore, it would probably be more prone to leaking. They seal to the bore with a thick o-ring.

If I remember right there is a battery heater blanket/wrap out there, it would be easy to install one. A warm battery and proper cold temp oil viscosity should get you started easily!