This macro is good when the boss spawns weak adds that dont die in one shot, but die quickly non-the-less (Garuda feathers for example). What it does is cast flare the first time normally, then immediately gives you mana and instant casts it, then transposes so that a second later you have mana again to resume your rotation. So far it works for me! (not recommended with normal trash in instances as you may likely pull the aggro)

You will have to have Astral III up yourself tho,

/ac Flare <t>
/wait 4
/ac Convert <me>
/wait 1
/ac Swiftcast <me>
/wait 1
/ac Flare <t>
/wait 1
/ac Transpose <me>

It's also just plain fun to cast Double Flare x)