/click worked. Haven't tested Poyzon's idea.
Here's the macro:

/click GroupLootFrame1GreedButton
/click StaticPopup1Button1
/click GroupLootFrame2GreedButton
/click StaticPopup1Button1
/click GroupLootFrame3GreedButton
/click StaticPopup1Button1
/click GroupLootFrame4GreedButton
/click StaticPopup1Button1
Works with up to 4 roll items dropped at a time.