The way I have discussed implementing this in the past, the code keeper would be the account owner.  SOmebody opens a new NXT account, then has the option of putting a freeze code on the blockchain telling all nodes to reject any future withdrawals from the account until that freeze code is nullified by the user sending a second message to  the blockchain containing a unique password that only the user knows.  That way a whale doesn't have to worry about his account getting cracked by doctorevil, if that happens doctorevil doesn't know the second password to enable NXT to leave the account.