Yesterday I made a post about how you can effectively send mouse clicks to other slaves. I guess I should have labeled it better than my multibox setup, but it has good info in there.

I use HotKeyNet and basically, what it can do is listen for a on screen LButton or RButton click. You modify the script to tell HKN if you click within a certain area X=100+30 Y=100+30 and if you do, it then maps that to a key and sends it to a slave window. On the slave window you create a macro, set it to a button, and keymap it. So, when you click and send F1 to your slave window, it reads it like you hit the F1 key.

I have a 3 man with a Paladin, Shaman and Warlock. Still learning a lot about multi-boxing and the best setup, but right now the Shaman and Warlock have a 4X3 12 button rectangle on my Paladin's UI where I click on a dummy macro and it send the real command over to my other characters. Works pretty well as it is pretty much a virtual keyboard. If you want any more info, I can share the script.