I have this set up.

The pieces:
- Melee toons in an Action Target Group.
- a Mapped Key (no hotkey) which sends IWT to the Current Window only.
- a Do Mapped Key action, in some of the spammed keys, that does the IWT (previous point) for Group (all of) the Melee Action Target Group.
- another Mapped Key with two steps, that activates (step 1) and deactivates (step 2) the Mapped Key that is inserted into our spammed dps keys.

Keymap Actions > New Mapped Key State Action.



Consider pop up text for the two step toggle.
So you know which IWT state you're in.