Thanks Angelica - I have added my vote to this issue.
Can you provide more detail on how to enact the following?
"Even if he is an internal user, the admin can remove the Service Desk license and let this user in the role "Service Desk Customers" in the project, so he will be able to access the tickets where he is the reporter or participant through the customer portal only. "
I have some managers that I would like to be able to invite as helpdesk browsers/commenters.