Blizzard has given the API functionality for an action on key down, and another on key up.
This has been included in the latest IS Boxer build.

If you want to take advantage of this, you need to click on the keymap in question, and change (drop down menu) the option from "execute on key release" to "execute on keypress or release".

My original example, was a two-step keymap, with a distinct output key for each press, and two physical press and release actions. Example H, in my guide has been updated to show a better way to do this with IS Boxer. You are free to use either two presses of a key, or key up/key down actions; either way it is still a two-step keymap.

I've included a keymap to toggle Click to Move on and off, which effectively turns IWT on and off -- even though it is keybound always. And of course sending IWT to your melee toons only, instead of the casters on your team, is a decent improvement too.