Enable click to move on the slaves.

Interface - Mouse Options - Check the box.
Or /console AutoInteract 1 (AutoInteract 0 = off).

Then have an Interact With Target keybind on the slaves.

Target something with the Healer.
Have the slaves assist the healer.
Press your IWT keybind, ideally one for just the slaves (possibly have two, so you can IWT the entire team too).