I've never done that, but I THINK the only way to do it is by selling the entire entity it's registered to.
The account is tied to a federal id number, and I don't know if that can be changed once it's set up. You'd want to find out from Amazon if that's the case, but even if it can be changed, you want to consider any tax consequences. For example, if you were to transfer the account in October, my guess is that the full year of sales would be attributed to the new owner.
That's something I don't know the answer to, but you should look into.