This is the way I have found to be most effective for my guild group to get Vorgannoth to the zone in.
We usually set our group up on top of the hill and start clearing all the mobs to the entrance of the building. Respawn is very quick, I have not timed it off hand since I do this usually by "feel" but I think the Ruins mob respawn at around 15 minutes, so once you start killing you can not stop until you have made it past the big room.
Once the mobs at the tunnel entrance are cleared someone active Vorgannoth and he will begin walking up the hill to the entrance. It is important that before he nears the entrance your enchanter mez him away from the doorway. In a pinch you can root him off as well. Your main goal is to simply stop him from taking his suicide plunge through the packed room.
Vorgannoth is a weak hitter and has little resists so having an Enchanter along will make this quite simple. Whenever your group needs to stop to clear more of the path ahead, simply have your chanter mez and or root Vorgannoth to stop him from moving ahead. Clear some more mobs so you can move up, then memory flux (mind wipe aggro) Vorgannoth and you can move him up some more, always staying a step ahead of respawn. (much like an old school Hedge run)
Vorgannoth walks up the right side of the room so if your group is careful with pulling and positioning you can avoid the opposite side aggro. Once he is past the main room he usually aggros one of the two hidden spiders from their aclove, then heads right for the zone in.
If Vorgannoth dies you are more or less in for a long wait (up to an hour).
At times we have helped another group clear the way into the instance while they had the task active. As soon as the group with the active task zoned in, a fresh Vorgannoth would spawn at his spawn point where someone was waiting to activate him, he would then walk safely though the cleared path to the zone instance with no delay at all.
I have heard of a class with invulnerability training the spiders around the water front, this is something we have tried once without success, but is certainly an alternative method of getting Vorgannoth to the zone in.
That is how I do it, I hope the insight helps someone