I use the following macro:

#showtooltip
/use Findle's Loot-A-Rang
/click StaticPopup1Button1

Usually in my case, 3/5 toons will loot the first time, then I wait for the Loot-a-Rang cooldown(3 seconds), hit it again, and everyone has loot. And this is not my creation. Full credit to Multibear/Deimon on the Isboxer forums.