Improving winter Hybrid performance

As a 2 time hybrid owner, I have noticed that due to the need to keep the engine warm in the winter, the engine runs more, thus burning more fuel than it would have done during a warmer climate time. Why not offer an option to add an airflow restrictor to the radiator to limit how fast the engine cools down in cold weather. I see this on road rigs from up north all the time. It could be electrically controlled and operated or a simple 'old school' water thermostat attached to the water coolant system. Placed between the grill and the radiator, it would be out of sight but most effective. I currently use a piece of cardboard with a few cut outs behind my radiator and my average mpg has gone from 37.1 back up to 38.7 . If it was an offered option, I would have bought when I purchased my second hybrid Fusion and anyone who has driven one in the cold probably would as well. I would even buy it now as a Ford addon. One last thing, I would include a manual disconnect, just in case it was to jam shut and start to overheat the engine.