How do I create a second email address under my Comcast/Xfinity account

I have an Comcast/Xfinity account and email address, say [email protected]. I need to create a second email address under the same Xfinity account, say [email protected]. I don't want to add a preexisting external email address, e.g., a g-mail address, but rather a secondary Xfinity email address under my Xfinity account.

The recommended help topic is "Manage User Roles and Permissions," which is silent about email. The instructions there for adding a Manager account want me to supply an email address for that account so that Xfinity can send an invitation link to that address. The "manager" email address doesn't exist yet. Creating it is the point of the exercise!

Am I in the wrong place? Is there a simple and direct way to create a secondary email address within my Xfinity account? What I want to do is click a link, supply a new email address, supply a UID and password, and voila, done.