Burning Wheel has a nice system of gaining traits. Other players suggest them based on how you play your character and with enough agreement from the group, that trait becomes part of the character.
Tonight I'm going to smoosh that into the opening section of our Diaspora game. Diaspora allows a player to change one of their character's aspects at the start of a session. We have a new-ish player who wasn't with us for character creation so he's missing a few aspects from his character. He's been with us for two sessions so we've seen a bit of the character. I'm going to ask each other player to suggest an aspect for the new character, based on what they've seen or perhaps what they'd like to see, and if the new-ish player agrees then he gets the aspect.
Let's see how well it works.