I did the same thing over the weekend. Had to call in, then pass the phone to my brother so he could create an account and register the unit to it. I couldn't find a way to do it online.
No TiVo account xfers of any kind can be done on-line, only the activation of a new TiVo or the activation of a non-activated used TiVo can be done on-line.You have to call them. Lifetime transfers can't be done online.