[Phantom]

I do not think that the tube would have to be very big. If a tube say the size of a garden hose or slightly larger were ran from the back of the engine bay to the side mirror and is terminated just before center with the outlet facing the front of the car (for diffusion) it could do a few things. First since there is lower pressure behind the mirror it would create a vacuum pulling air from the engine bay, along with this it could help reduce high pressure in the engine bay especially if it has a full belly pan. Once the car is warm it would work as a passive defroster. Also with the smaller tube it will not be able to move a lot of air but should have decent velocity.