To me, though, there’s not really an issue with the original. And I’m sure there’ll be EU stuff to fill in his story.
I suppose it’s possible that as a moody teenager he ran away from home (the Resistance) and joined up with the wrong people for a while. In fact, I wouldn’t be surprised if that’s the canon answer eventually.
EDIT: Sherlock, you writing that out made me realize how much of their funny banter you would have to cut out to make this work. As much as I would like to get rid of this to avoid stereotypes, I think I’m gonna have to agree with Hal here.