This trick requires at least 10 minions. When you reach the troll, you will get 
a cutscene of him getting ready to fight you. After that, have all your minions 
rush to open the gate by the crane. If the troll is blocking the path, just lead 
him away, and go through the gate. The troll will probably kill a few of your 
minions as they open the gate; however, it takes approximately 20 to 40 minions 
to kill him on the Legendary difficulty. Once you open the gate, go to the crane 
to auto-save. After you auto-save, the game will assume you defeated the troll 
since you went further than you were supposed to. Simply leave the area and come 
back, and the troll will not be there anymore since the game thinks he has been 
defeated.