Hello David,
Sorry for the delay! You can always change your email in your account to any email that is not in our system already. Duplicate accounts for the same email are not yet permitted by our login process. What your colleague can do, however, is change their email address in their free account settings to another email. You will then be able to change your email login to the original email of your colleague. If you have issues with this process, please email help@moz.com so we can maintain account info confidentiality.
Have a great day!