I don't recommend applying regen before a boss pull. Not like it matters much for bosses, but here's an alternative:
Apply Stoneskin before pull -> Pre-cast Aero III to land on pull -> Aero II -> Aero -> Assize+Fluid Aura -> cleric off -> Regen -> Cleric on -> Presence of Mind if you want -> Stone III spam -> Aero -> Cleric off -> Regen + tetra -> Cleric on etc.

You can queue to toggle off cleric while casting something without losing GCD time. Only applies when turning it off, though. Turning it off involves animation locks