I'm no expert, but it sounds like you would be needing a reseller account. In which case, you could do what you are talking about using the Web Host Manager.
Doing it without being a reseller sounds like you would have to purchase/transfer the domain, buy the TCH account for client, and then you would have access to a cpanel for that account.
But...I could be wrong. I'm sure someone more enlightened will verify. Thumbs Up