Since is this reassigning a single question's ownership, moderators cannot do this. They can merge accounts, but that would leave only one account.
The only way that this could be done is by a developer. If they do not see this question, you can email them at firstname.lastname@example.org, but there is no guarantee that they will be willing to do this for you.
However, even if they are unwilling to do this, remember that it's only one question. You get the reputation for taking the prerogative to ask the question, and I'm sure your friend appreciates getting the answers even if he's not getting the rep. And since you've introduced him to the site, I have no doubt that he'll ask his own questions and build up his own rep anyway, so it's not too terrible if the devs decline to do it.