multiple domains and email addresses for same user

i have two domains i added to my office 365 account (worked perfectly). here's the issue:

i want to have separate email accounts (one for each domain) for one user.

joe@domain1.com
joe@domain2.com

i don't want to setup aliases. i want a new email box. Do i have to make a whole new user just to get that new domain email? that seems really clunky. So i will have duplicates of users with the same name not to mention having to pay another $13/month for the email account.

thanks!