Hello there , well i just found out this bug on a private server , while doing a SWP run with my guild so i decided to share it. Works on Mangos last rev.
Basically you need to be a class with Insta aggro removal spell (Hunter's Feign Death and Rogue's Vanish work i've tested both).
Basically you need to pull a group of mobs and than use the spell.. it should make them stuck near you .. than all the people who run trough them wont aggro unless they are attacked.
Quick version:
1. You need a hunter or a rogue
2.They run in the trash mobs and move a little bit backwards
3.They use feign death/vanish
4.Mobs get stuck and wont aggro anyone who passes near/trough them
Using this exploit enables you to skip the mobs and directly go to the bosses , depending on how fast/many hunters/rogues you have.
Doesn't work on scripted Sunwell Plateu instance.