This works for both factions.
It's pretty simple, say the buff goes out at an inopportune time for your guild. Have a Priest from the opposite faction Mind Control Major Mattingly or Overlord Runthak, kill the MCed NPC. He'll respawn in roughly ~5 minutes. After he respawns you will be able to turn the quest in and get Rallying Cry of the Dragonslayer regardless of how recently it was turned in.
You have to kill him each time if you'd like to turn it in before the 6 hour CD.
For PVP servers this is easy to coordinate on Server Discords. A majority of servers have them.