If he also possess the recovery key it will be infinite war to login/change emails. However if the registration is on him he can simply order a CK and wait for it to arrive, and eventually get a new RK. Not much you can do before the registration is on you. He can always just order new CK if the registration is on him.
/Stusse
Let's hope he lost it..
I will just not use this account for 1 month and wait.