He would have to pick a passenger with no friends and no family. Dont forget, these people are famous. even if someone had a job, no friends, no family, no nothing, and he were killed in a plane crash, when that person resurfaced after living on an island, you (as an employer or co-worker) would take notice...and when that person was actually someone else all together you would probably speak up. With as famous as the Oceanic 6 are, I dont see how anyone could assume an identity. If they could, Kate would have been the first in line. Sawyer too (who I believe decides to stay on the island with Locke) Just a thought - since Locke has no friends or family to speak of, what if Ben assumed his name as his alias? Locke's con artist father is dead, he grew up in foster homes, and worked for a "box" company. Would anybody really care if he was a survivor and seek him out? I don't think it's likely, however, since the survivors would be celebrities upon returning and would be frequently photographed - making it easy for whoever is hunting Ben to find him.