Summary

These are some pieces that allow you to convert the standard extruder setup into a bowden setup.
This is a mod for 3mm filament.

UPDATE :
Added dual-hotend versions so you can start experimenting with multi-color printing !

Instructions

Minimal instructions if you have a stock printrbot

print a extruder-to-bodwen and a bowden-to-hotend
Install the Pneufit adapters on your bowden cable and screw it onto the 2 printed pieces
install this on your printer

Extended instructions - if you're feeling adventurous

If you want to mount your extruder to the x-idler, print the gregs_to_bowden-X-idler.stl instead of the regular one. It can hold a horizontal bearing and fits over your z-axis ( on the X-idler side )
If you have a reprapfab hotend, use the bowden-to-hotend-reprapfab.stl file

Experimental instructions - to go where no one has gone before.

If you want to experiment with 2-color extrusion, you can also pick a dual-hotend bowden-to-hotend version ( I rendered a regular one for a UBIS hotend, and a reprapfab version , with 20mm distance between the extruder tips ). This was never tested, and would most likely require modifications in the electronics and software to accomodate an extra extruder on a printrbot.
But I'd love to see somebody take this challenge !

Notes:

I used 50cm of PTFE tubing, 3.18inner/6outer diameter (10cm)
http://reprapworld.com/?products_details&products_id=166

And 2x Pneufit straight adaptor,1/8inx6mm
http://reprapworld.com/?products_details&products_id=168

And a UBIS hot-end ( stock Printrbot extruder )

The bowden-to-hotend is just a modified version of the Greg's Wade reloaded extruder body, so you can create hotend mounts for any supported hotends ( malcolm, groovemount, arcol, mendel_parts_v6, jhead, reprapfaborg and others )
If you want to modify the bowden-to-hotend, you'll need the configuration.scad and jonaskuehling-default.scad include files from Greg's Wade Reloaded ( http://www.thingiverse.com/thing:18379 )

Printrbot Bowden Cable mod