Sorry for long name.. but here we go.
Necromancers that spec into the reanimation tree get a spell called "Unholy Hands". it's a channeled spell with a 75mana cost, and 45 second cooldown. It does around 200 dmg per tick. What you do it cast Unholy Hands normally once, then just spam your hotkey for it + click where you want it to cast at while it channels the initial cast. What happens is, the 45sec CD doesnt start until it ends the first cast, but you can precast in this game, allowing you to put another one up before the CD enables.
If this is too hard to understand, ask questions, also.. you can do this with other channeled spells with long cooldowns, if i'm right that is.