Get a priest and this item, Draenei Fishing Net - Item - World of Warcraft, then get inside BT or your desired raid boss etc... and go to the mob that is locked, for example, on Tox1c, illidan is locked because akama was deleted, using wowemuhacker if needed
next, spawn a murloc using the net (double click it fast as much as needed)
Mind control the murloc using priest
Attack the mob (Illidan in this case)
Voila, aggro'd locked mob
Now he functions like any other mob. This works for any mob you can't attack... actually. ^^
Working on ascent 4.6+... tox1c-wow as well.
Credits to LiveHiFi @ deathsoft