New XBL account. Transferring stats etc

Hi.

My son has been playing Ghosts using my XBL account for several months. I have bought him his own account now, but since he started playing on his new XBL account he says he's lost his stats etc. Like before he'd prestiged, but now he's back at the beginner level.

Is there a way whereby he can transfer his stats so he is back to where he was before he had his new account?

Thanks