I suggest to add a simple text field, that allows to name any recipient desired. FinalBuilder supports this using a comma separated list for e-mail notifications. This is actually a requirement for us, as we need to notify people, that are not registered users of ContinuaCI. A simple text field will support this easily. It’s also flexible, as it does not require to create permission groups, just to support notification groups.
Generally build notifications would contain a link to the build view page in Continua CI. If the recipient is not a registered user, then they would not have access to Continua CI to view the build details. Why not just add them as a user with minimal permissions?
Otherwise, we would recommend adding a FinalBuilder Send Email action to the end of the build to send any emails to recipients who are not registered users.
Adding users, just to be able to send them notifications is a viable solution. I don’t know about Continua’s licence model, though. This is no problem?