It might work better if you made a 'tunnel' and used a single 120mm or 140mm fan on each end (much like the Antminer S3).  This way you're forcing the air through a particular path no matter what's in the way and it won't be deflected/scattered about.

The problem with the tunnel idea is the frickin' wires that come out of both ends.  I could do it with mine fairly easily because I relocated the power connector to the other end where the fan and usb are.  So I have one end that's connector free.