I went through all the scenarios myself since I got no reply, and it IS possible.
Step 1: Tell both sides your working for them (lie to Azkul, let Vrook run peacefully in the Kinrath Cave).
Step 2: Do whatever you wish in terms of sabotage/repair. I sabotaged some stuff while I repaired other stuff.
Step 3: Initiate the battle via Zherron. Vrook will run off to delay the mercenaries.
Step 4: Fight the mercenaries.
Step 5: Once inside, side with Azkul, letting the mercenaries win (in fact, only this decision of whether to help Azkul or the settlers matters - everything else has little to no effect on the result).
Step 6: When Vrook returns, he will lament that the overseer is dead and that you lost, but since he was gone, he will have no idea that you changed sides. Thus, he will not fight you.