This model adds a bowden mount position in front of (-Y) the existing Wade's extruder. I'm using this in my Printrbot Plus Dual Extruder project to add a 1.75mm bowden driven extruder in front of my stock 3mm Wade's extruder. You'll still need to add a bowden-to-hotend mount. I used http://www.thingiverse.com/thing:104005
The x-carraige was adapted from noreway's Printrbot Plus Quick-Fit Upgrade(http://www.thingiverse.com/thing:96230)
Getting the two hotends absolutelty level (i.e. the nozzle at the same height,) is critical. I used washers to shim since this is still experimental. Eventually I will combine the Bowden/Ubis mount into this frame.
The OpenSCAD code is not pretty, I need to return to it and clean it up for broader consumption.
I printed at a .8 infill to make this a very solid piece. Don't skimp, this needs to be very rigid.