UPDATES
6/4/14 - I've added a v3 STL file that increases the room for the fan and removes the support structures since Slic3r now has better support generation.  This is untested so if you print it, please comment on your results.
Original v2  - while the 2 breakout sections are somewhat difficult to remove, the diagram does show the breakout sections - just do it slowly and carefully. This cooling fan has been in continuous use for 2 months now printing cameras from my Kickstarter Pinhole Printed project (www.pinholeprinted.com). It works very well and as yet, I have not seen a need to improve on it by using a second fan.
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This is an experimental cooling fan for my E3D, mounted in a Solidoodle 3. The original hot end plugged up once too often and so I installed my E3D, which works really well. However, the E3D has its own fan and the size makes mounting a separate print cooling fan difficult. So I combined the two into one 40mm fan, which runs continuously. Two-thirds of the airflow goes to the E3D heatsink and one-third is diverted to cool the print. There's no control over the airflow to the print. It's not perfect but it works pretty well and doesn't reduce the build volume of the Solidoodle 3 anymore than the E3D did. The cooling circle is partial to allow for the E3D heater and thermistor wires. 

Be sure to line the inside of the cooling circle with foil HVAC tape or fiberglass high-temp tape to insulate the plastic from the hot end radiated heat. Print in ABS - not PLA. There are two integral supports that need to be cut out, see the yellow sections in the CAD photo. They could be easier to remove but I haven't taken the time to make them easier since I think this design is a waypoint to a better one later or by someone else. 

I printed this in ABS at 205C with 0.25mm layer height, 30% infill, and 4 perimeters.  Note it takes a LONG time to slice - on my notebook, it took 58 minutes to slice using Slic3r.

Update:  I've had no particular problems with the cooling flow being always on.  It works for me on my Solidoodle 3 and it's better than the stock E3D fan.