Custom watercooling to an outdoor radiator? Only issue is it would probably push block temps below ambient in the house and you might have to worry about condensation on the board.
I think it was Linus Tech Tips that decided to plum four or five machines together and have it all watercool outside.
I was thinking it might be nice to pick up a car radiator and have the stupid thing running passive outdoors. Might even be able to run the fan off 12v, depending on the amps (Google says ~3A?). I've been toying with similar ideas in my head, but it seems like a $50-80 for a radiator (new?), an
$11 digital thermal relay,
12v PSU, misc parts and fittings.. could end up with a wicked awesome, dead silent cooler. Only issue might be corrosion with the radiator likely being aluminum though.