IF (and I accept it's a big if) the rear 120mm fan lines up with the cpu socket then you may be able to use the Thermalright HR-01 and the 120mm fan duct. This basically turns the rear case fan into the CPU cooler fan using a very large passive 6-heatpipe heatsink.
http://www.thermalright.com/a_page/m...t_hr01_775.htm