Dual zone heat bed ??

I have been pondering and thinking. It seems that I tend to want a fairly large heat  bed build surface both my printers are 8" x 8"  and to me a 8" x 12" would be ideal. yet most of my prints are smaller than 4" x 4"   does anyone make or have a dual zone heat bed that the center  is one heat zone and the outer perimeter is a second zone? that way one could save power when doing small prints but when the whole bed is needed the full bed could be heated.  Would this be practical and economical to produce? I know it would need two control circuits and a second thermistor.
Tin