List collector field with email option in Service Catalog

In other tables the Watch List list collector object can also have an email box, for typing in emails directly which are not.

I'm working in the Service Catalog, and would like to provide the ability for users to select a user from a list collector, but also to add an email address directly should their user not exist or have some other reason for needing notification.

Is this possible? (I've read in some other threads that it is not, but many of them are dated and I am surprised that it is not).