Warden's could be an AOE song that stays up indefinitely and removes a chunk of MP each time it blocks an effect. Can't be played with other songs (except WM) so you could potentially have it up when Foe's and resource regen isn't needed. Maybe for balance, MP regen could be slowed/stopped while playing to prevent 100% uptime.

I'm not sure about the rules regarding name-dropping other games, so I'll say it this way: A certain other MMO I played had an option added where ground-target AOEs, if you just double-tapped the skill's hotkey, would simply be placed on top of the current target, centered around them. I think that'd work for things like Flaming Arrow.