The wizard gets you a CTM, which turns on when you press the key and is disabled when you release the key.
On its own, a two-step will work great.

But when it is called as part of a Do Mapped Key function, it doesn't work so well.
The entire two-step is trying to be done as one step in another mapped key that is calling it.

I would go with this approach:
- enable CTM all the time, at least for melee teams.
- put the melee into their own ATG.
- create a mapped key that sends your IWT Keybind to the Current Window.
- add a step to your existing DPS keys that is Do Mapped Key (the IWT Keybind mapped key) with a Target: All members of the melee ATG.
- modify the DPS Keys to execute a step on press or release.
- create a two-step toggle that enables (step 1) and disables (step 2) your inserted Do Mapped Key action.

In practice we have.
- You push "1" or whatever DPS keys you have added IWT to.
- It does the FTL Assist and sends '1' to all windows.
- On the release of the key, it sends IWT to your melee toons only.
- Because CTM is always on, they move to the target.
- When you don't want IWT auto spam, press your toggle key.

I've added text pop up actions to my toggle key, announcing whether IWT spam is on/off.