I've been using this for awhile along with http://www.thingiverse.com/thing:442636 and http://www.thingiverse.com/thing:383713, they all took a little tweaking but have been working great (and out of PLA no less!). I really wanted to try a dual extruder setup and since this one (http://www.thingiverse.com/thing:457528) looked awesome but a lot of effort I remixed the part '1405AlExtruderFront-Short-2014-06-24.STL' into this: http://www.thingiverse.com/thing:696955 . It's basically the same part but I cloned and mirrored the extruder area and stuck it on the front of the existing extruder. I'm not a CAD expert but it should work to hold a second extruder. I haven't tested it yet but I thought I'd mention it since I'm sure iamjonlawrence could shame me with his CAD skills and pop out a much better one than I knocked together.