I wanted to get a second fan on the EVGA superclock to see if it made any difference in the temps...and it does make a difference. Since ambient room temps were different before and after I can't post any definitive temp changes, but I can say the difference is as much as 5c lower on avg across all 4 cores with a 120mm Hyper 212+ fan on the back of the Superclock cooler. The biggest difference seems to be in terms of noise output. With just the Superclock fan, it ran at 100% (to cope with a pretty agressive dose of overclocking) but with both fans attached, neither are at max rpm so it is actually much quieter and this is the biggest benefit as far as I'm concerned.
 
My initial idea was to thread four 6-32x4 machine screws through the mounting holes of one fan and into the other, but this does not work with the Superclock because a heat pipe is in the way on either side of the heatsink exactly where the screws would need to pass through.
 
So the idea that seems to work best for me is to use a pair of $2 extension springs with hooks on both ends an simply use the spring's force to hold the puller fan in place. I simply hooked one end onto the fan mounting clip that came with the EVGA cooler and the other end can be hooked onto the other fan in any fashion. Some pics:
 

the 3rd  hole should theoritly let you put one in pull but you need another clips
 2nd one is for a 120X38 as i demenonstrated in my post

look in your bios for smart fan settings. turning it off will run the fan at full though so you would need a fan controller to adjust it then.