Two accounts

Anyone know how to link two accounts?  I have one for our home and one for our vacation rental.  I cannot integrate the two through one user name and one password.  So I have two usernames and two passwords (one set for each account) but then when I try to register my mobile phone and my email with the second account, the systems says "that is already linked to another account."  No kidding.  

My bank, investment broker, and even BGE link all of a customers accounts under one profile, but apparently not Xfinity.  I can't be the only customer with multiple accounts.  Any suggestions, ideas?