I appologize for not posting the correct macro. I logged into the PTR tonight to get this working. This is the macro that you want for your clones. I only tested this on my priest by manually pinging the minimap, and then using the macro. The spell hit where I pinged on the map (but up in the air). Once again, you will want your secondary toons to use the macro a little after your main so they have a chance to see the minimap ping.

Code:
/cast Mass Dispel
/script local x, y = Minimap:GetPingPosition() Minimap:PingLocation(x * 140, y * 140)