On a nuts an bolts level, you'd have an insulated reservoir conataining about the same volume of fluid that your cooling system uses. When you park, you'd pump your warm coolant into this reservoir (cold fluid being pumped into the engine), and before you go again, you'd pump in back into your cooling system (cold fliud pumped into the reservoir). You'd be using an electric pump. I figure a hobbyist could rig it up with a couple hundred in parts.

This is an excellent idea, of particulat usefulness to the commercial trucking industry, which utilizes large displacement engines. In extreme cold, it is commonplace to allow truck engines to idle continuously when not busy moving the truck/trailer. Continuous idling produces imperfect combustion which increases engine wear dramatically. This system would circulate coolant that was at near operating temperature when it was time to restart an engine that had been shutdown.

An additional benefit of this system is that having an electric pump would greatly simplify coolant changes, doing away with the mess of pulling off hoses and having coolant splash all over the place.

A German engineering firm is introducing an electric coolant pump to replace the fan belt driven pump that is common to curret internal combustion engines.

This would be a perfect addition to such a system.

There are some coolant pums for the regualr operation of the cooling system that are electric. I see them available to the custom automobile industry.

The pumps for the reservoice<>engine I propose are DC utility pumps, which I suppose could handle engine coolant (I'd have to look into the chemical compatibility of the pump in mind)

Here in Helsinki where the winters can get to 30 degrees below freezing in the winter, most people have electric plug-in points where they park and use a time actuated electric heater in the car to pre-warm their car in the morning. No pollution.