You need only a range pet (maybe melee would also work, but i don't know)
1. stand on the ladder near the boss
2. command your pet to attack the boss
3. release pet
4. come closer to the boss
5. bring him down to 3-5%
6. come closer to the boss, he will enter combat
7. kill the boss
8. ...
9. Profit!
video of the exploit: