There was a post or statement somewhere (sorry can't provide the link) that there will be an option to set a 'personality' for one of the characters and they would auto select their options. I think this is the feature you want. Unfortunately I do not know when (or if they still intend) to provide this feature but I'm fairly hopeful it will be provided before final release.
So after about my 3rd time playing the game (after patch changes etc). I am curious if, as someone playing solo atm, I can set one of the two main characters to choose it's own dialogue.
As of right now whenever the two player dialogue starts I have to choose the dialogue for each of the main characters. In many cases I now have to argue with myself. It's not very fun (I always win) and I feel like it takes the immersion out of the game.