Update 10/04/2017: Added photos showing clearance at X200 Y0. It comes very close to the frame, but makes no contact, at least on my machine.
Modified 50x15 blower duct by claancy with a view port (I just cut a chunk out of the front so I could more easily watch the first layers of prints go down).
It's probably not ideal, but I haven't noticed any decrease in performance.
Works fine in PLA as long as you are only printing PLA. Mine started to sag after I started printing in PETG, so I printed one in PETG and it's doing fine.
Only print supports touching build plate to support the mounts on the back, otherwise you'll never get the material out of the duct.
I opened the model by claancy in NetFabb and used the Free Cut tool to make the view port, then I sealed off the now-open ends with a few polygons and merged them with the main model.