We will probably end up trying a watercooled system using PC parts due to the socket size... should at least look cool!
Are there are quad head water coolers out there? That might be interesting.
Either buy a 9x120mm and or a 4x120mm radiator - with proper thickness and heat removal capabilities.
If you can put enough air through the 9x120mm, and run a few loops it should be possible to cool 2x4minion boards.
Remember a good size tank also.