I’m not sure if that’s possible in Workflow out of the box, due to the way that Emails are stored in the CRM
As far as i’m aware, they’re stored as such:
Email record in the “Emails” table -> ID relating to the “emails_email_addr_rel” table -> ID relating to the “email_addresses” table that contains the Email Address (to/from)
You might have some luck building a logic hook to do it, as you'd have much more freedom
Unless another user perhaps has an idea of how to add this field to the Workflow options?