Conditional cast based on pre-existing stacks?

Is there any way to use the stacks of a given buff to determine if you will cast that buff again?

In particular, I’m looking at Focused Rage in Arms Warrior, that takes 15 Rage and adds a buff my character up to a limit of 3 stacks. Any further casts are accepted but don’t increase stacks, so the Fury that is used is wasted.