Freddie just introduced mouse triggers to HotkeyNet which allows one to use AOE targets across multiple clients. To test this I first readied the spell on a warlock and a hunter with a hotkey. You could do that with whatever you are currently using to broadcast keys, I assume. You have to have each of your alts facing the same direction, obviously. That can be done with a SetView macro if needed. Using the code below as an example you could have your main toon place a target with the mouse and then click Grave+LButton to have the alts fire away. HotkeyNet positions and scales the cursor according to the main so it doesn't matter if you are using a different resolution. I just did this for the first time this morning so I can't offer a lot of tech support. I was hoping we could all pitch in to perfect it.

Code:
<UseKeyAsModifier Grave>

<Hotkey Grave LButton>
<SendFocusWin>
<MouseClick LButton>
<SendWinM LWoW1>
<MouseClick LButton>
<SendPC 192.168.1.8>
<SendWinM RWoW3>
<MouseClick LButton>
Edit: I'm assuming this is legit. Please advise if not.