There may be other ways to do this, but if you're sitting at a boss (after wiping a bunch) and there's no critters or trash to attack, you might be SOL for getting Holy Power.
The best way I've found to generate HP before a boss starts is using the Holy PVP 4-Set (522 Grievous Gear from MOP). Even as Ret you can equip this 4set, spam Flash of Light on yourself and generate HP. I recommend doing this as you're running back to the boss so that your mana regens & you just stop running to Flash of Light every so often.
Once you're at 5 HP you have to worry about the decay of HP so just cast a Flash of Light here and there until the boss fight starts so that you have all 5 up.
Then you can start the fight with 5 HP, trinkets & full CDs for even more burst than you pull now.
Enjoy - Hope this helps you if you didn't know of this already @NotYerPalGuy
The best way I've found to generate HP before a boss starts is using the Holy PVP 4-Set (522 Grievous Gear from MOP). Even as Ret you can equip this 4set, spam Flash of Light on yourself and generate HP. I recommend doing this as you're running back to the boss so that your mana regens & you just stop running to Flash of Light every so often.
Once you're at 5 HP you have to worry about the decay of HP so just cast a Flash of Light here and there until the boss fight starts so that you have all 5 up.
Then you can start the fight with 5 HP, trinkets & full CDs for even more burst than you pull now.
Enjoy - Hope this helps you if you didn't know of this already @NotYerPalGuy