There is a way to do it in the Vanilla WoW interface, but you have to use the right syntax. If I recall correctly:

ActionButtonX
BottomLeftActionButtonX
BottomRightActionButtonX
LeftActionButtonX
RightActionButtonX

X is 1 through 12. ActionButton is your main bar, Bottom Left and Bottom right are for those action bars, and left and right refer to the 2 action bars you can put up on the right side.

Assuming I got the syntax right there.