I just got ground-based AOE targetting figured out on my group of 1xpally,1xPriest, and 3xFrost Mage - and it's very very good.

I use hotkeynet (free, and awesome, btw) to control both the keyboard command that tells all 3 mages to cast blizzard (or flamestrike or whatever), and the mouse click that tells them exactly where to place it.

I use the ~ key as my modifier, and simply hold it down and click in the middle of my screen to send the "mouse-click" to the relative coordinates on the screens of my 3 mages. It works great! (see http://www.hotkeynet.com/ref/clickmouse.html ). There more that you can do with hotkeynet, but i'm only using the basics =)

The key to getting this working effectively (no matter what software you're using), is to have the view set correctly on all your clones - i use 100% top-down view and zoomed out (not at an angle).

I used to have arcane-explosion+consecrate+holy-nova all mapped to a button that I would spam, but the 3x mage blizzard is much faster, and SO much more mana efficient.

Let me know if you're interested, and I'll send you the hotkeynet script I use.