Inside the bottom of the fridge, place a wide, flat, copper or stainless steel water tank with two pipe connections. Flexible, insulated hoses pass out through two notches cut into the bottom door seal. They pass into an insulated drawer below the fridge, and connect to another water tank attached
to the lid of the drawer. When the drawer is pulled forward, the lid swings open, hinged at the rear.
Water in the upper tank is cooled by the refrigerator, and sinks into the lower tank, forcing the warmer and lighter water to rise into the refrigerated tank. ie: a thermosyphon cycle begins.
The lower drawer can be used as short-term cold storage for guests, for bargain bulk purchases of perishables, etc.
The drawer need not be even a permanent fixture, or directly below the fridge. It could be as simple as a disposable expanded polystyrene vegetable box, a cooler bag, a folding insulated box, or a drinks cooler. As long as the tank in the fridge is higher than the one in the extender, a thermosyphon loop is made possible.
Any kind of watertight container can be used for the upper and lower heat exchangers (tanks) - I suggested wide, flat and metal for the greatest heat exchange. Coiled or folded copper pipe is another possibility.
Yes, this will make your fridge work harder: it's not meant as a permanent solution. Keep the thermostat above its minimum temperature setting to allow for the extra work.