Find someone who has done BiC (at least through the Barindu portion). They will have sufficient faction with Yunjo slaves. They can get the dagger, equip it and attack Oltix. He will then drop the backflag parts when killed.
Yes, you can do the factioning yourself (via killing arena mobs in Riwwi and feeding the Yunjo slaves in Riwwi), but unless you need to kill Oltix via MQ2, I'd just find someone who has already done the faction work to attack Oltix for you.