I've recently had my eyes opened by a lot of systems that *require* player discussion. Dresden Files is so committed to player-discussed character creation, it's required *even for the pregenerated characters in sample adventures*. And I was *amazed* at how much extra depth of roleplay and character design emerged from just five minutes discussion between players.
This suggests it should be possible to achieve the same in D&D. I'd start with the Fiasco technique - don't just pick classes, but ask the players to add relationship backstory.