Provided we're adhering to the laws of the universe this is a solid plan in terms of energy and how it will behave. Provided the freezer manufacture hasn't deviated from nor altered their schematics as part of some nefarious plot to thwart my attempts to conserve energy it's also solid.
The variable here would be achieving a balance of using the "fridge" portion enough (opening the top) and adjusting the "freezer" portion to keep the top area from freezing. I'm guessing say 30 degrees down below may allow for this. I guess time will tell but somebody has to do the experimenting.
I can say that the bottom of my chest freezer is 0 degrees, the top of the lid (inside) is 12 and the top of the lid on the outside is 75 so it's behaving as I would expect for this plan to be functional.
The only caveat is that I'm kind of out there so you may all know better than me and as rkentzel mentions I may drill into a coolant line and end up dead over this but my family case sue GE (this is America after all) for not having their cooling lines where their diagrams depicted them. If you don't hear back from me assume the worst /: