Summary

super simple clip-on probe for use with newly released Printrbot auto leveling firmware. good luck!

Instructions

I printed this is in PLA, and with solid infill. Do as you wish.

Printrbot Marlin firmware can be found at https://github.com/Printrbot/Marlin/releases
with further instructions.

learn to flash the Printrboard firmware at
http://printrbot.com/support/instructions-and-guides/instructions-flashing-the-firmware-on-your-printrboard/

I used a normally closed button glued to the end of the probe, in series with the z end stop. If the probe is all the way in and flush with the aluminum extruder, the coordinates should be close to y = 0 x = 13 z = -10

so your input code should be something like
M212 X13 Y0 Z-10
Into the custom gcode area in slic3r.
make sure you do your own measurements, however. the z displacement is important!

Brook's article explains a few things fairly well.
http://printrbot.com/2014/01/19/printrbot-demonstrates-auto-bed-leveling/

Auto leveling Probe for Printrbot Plus / LC