It's a shame no sff power supplies some with an option to have the mains plug go in the side and not the rear. It would allow you to maybe squeeze a slim fan above the power supply but even without the cable it's probably to tight without modifying how the power supply is mounted. I was thinking you could maybe squeeze in a few 40mm fans under the GPU to get some air moving around, but the cuts outs would not be ideal. The only other place you may be able to squeeze one in would be behind the power supply as your using a short card, but honestly I'd get the system built and see how you get on with the single 120