I have a Hyper 612 with a cooler master jetflo 120 mounted with the plastic brackets as I don't think the metal ones will work as the screw design is enclosed with the jetflo 120, but it works great, the jetflo 120 has a high static pressure meaning more push compared with the stock fan and my FX8350@4.4ghz reaches almost 50 degrees overclocked and overvolted, I actually suggested cm offer the jetflo with the hyper 612 as a performance option. They work very well together, idle my cpu is around 24 degrees (almost room temp).
I had to tape 4 small pieces of carboard right near the screws on the inside of the fan to get it to mount tightly as there was a small gap making the fan bracket slightly loose.
I think you can mount a fan on the rear of the heatsink (not a jetflo 120) but it gets pretty close to the rear exhaust fan already (really really close depending on your case).
In total in my Core V71 case I have 5 jetflo 120's, one on the cpu cooler in pwm mode, one rear exhaust on a 3pin header with 19db adapter, and 3 intake (also on 3pin headers w. 19db adapters), one top front acting as a compressor at the top of the 200mm on the inside of the case and 2 lower intake fans. After testing one I bought 6 more, I have 2 extras just in case, don't know about longevity with these yet but they are a great fan.