Short version is, there's no easy way to do this consistently for all use cases. Lining up the cursors so you can broadcast click/IWM is one of the more annoying things we have to learn as multiboxers. With the node changes recently, you should be able to click twice pretty quickly and make it work.

You could also set up an "Interact with Mouseover" button, adjust your cursors first, then just press that key to "click" them all at the same time.

Doing this with hunters or other pet classes or on those quests where you have NPCs following you around is just maddening. I usually just run by the side of the thing, so my followers are in the right spot, then back up on my main so his cursor is in the same spot as the others.