I like this idea. Rigid insulation is often foil-faced; that seems like a good idea for the refrigerator side.When I do my baffle I plan to use tapered PolyISO insulation board that is designed for commercial roofs. 3.5" of that stuff has R value over 20. I figure that a solid (tapered to fit the curved wall area) baffle made from PolyISO board of the same overall shape proposed by Reace will keep the back of the refrigerator much cooler and result in better overall cooling performance.
I see that the 120V outlet gets buried behind the baffle, which seems like a feature to be avoided. Solid foam could have clearance for the outlet and cord carved out of it.