This version of the extrusion catcher has a little tab to attach the catcher to the bolt in the bottom left corner of the build platform. Here's a video of it in action: http://www.youtube.com/watch?v=8P1vekuYYgo
There is a pilot hole in the tab where you'll need to drill a larger hole for the bolt to fit through. You'll also need to trim the wedge support part of the tab so that the bolt head will sit flat against it. Here is my start.txt for reference:
M104 S210 T0
M109 S110 T0
G92 X0 Y0 Z0
G1 X60 Y35 (Move over the extrusion catcher.)
G1 X0 (Move over platform to start print.)
Rather than simply copy-pasting, you should experiment with the gcode to move the head by writing a small gcode script in ReplicatorG and then executing it. That way you can make sure it works on your bot before blindly relying on it when trying to do a print.