I made a small plate from a piece of PC board. I soldered a wire to it and hooked that to my probe input. I used the Z button script from a few replies back.
That worked so well that I decided to add buttons for touch off on X and Y. I used the standard screen for Offsets, and used the graphic there to indicate which edge I was touching off. I simply hold my little PC board plate against the correct edge of the piece and click the button. It seems to be working perfectly.
I used the same script for each button, with the obvious changes for X and Y. I did screw up one button and made the pull back move the wrong sign and snapped off a test tool. At least I know my new mill has lots of torque :-)
I set the feed to 1 in/min, rather slow, but then the overshoot of the probe after it touches the tool edge is so small it doesn't hurt anything. I jog up close to the touch point, less than 1/4" before touching.
Works well for nice edges, like a vise. Might be hard to hold the PC board up to an irregular edge.