Thats what Rage is for, probably the best 2min cd that’s been put in the game for awhile cause it allows you to pump the first 15%-20% of a boss fight then you ether pop Rage to continue the pump depending if the boss fight is long enough to pop rage again and if it isn’t you can probably wait to use Rage towards end of the fight and you get the full effect of mastery.
If you want a crap mastery, try playing ret the past 3 expansions.