It seems as though there is no way of creating an email for the end user when manually adding a Ticket.
Hi StevenJP,
We are planning on releasing the end-user portal in November, with the ability to create end-users from the admin portal. This will allow you to create new end-users and attach them to tickets.
We are also working on a feature to create new end-users and attach them to tickets directly from the ticket editor. This is currently planned for Q1 2023.