It's very simple really.

Group your Paladin, Warlock, low level toon.
Pull a bunch of mobs with you Paladin back to the zone in. DO NOT do any damage, shield spike, retribution aura, heal, etc. with any toon.
Remove the Warlock from the group.
Run the low level toon some distance away so he's not instagibbed.
Use Consecrate to get the mobs down to <50%, ideally 20% or lower.
Zone the Paladin out.
Blow everything up with the Warlock. Collect mad XP.
Reinvite the Warlock before 60 second timer is up.