I printed http://www.thingiverse.com/thing:214536 to use dual extruders but then my filament fan was too far away to do any good. So I whipped this up and it works like a charm. Requires http://repables.com/r/155/ stl file to compile the OpenSCAD script, but I've attached the final STL too. Repables doesn't say the license so... let me know if you think I've violated anything. Update: I found the height tolerance a little too close to my liking and it would tend to snag things that had any slight curl. I've posted a new one 1mm higher. If you want the old version just change the SCAD file.