The easiest method I could see this working, and still using the Service Desk portal, is to give the supervisor the ability to assign the reporter and watchers. However, I only seem to be able to see the 'Raise this request on behalf of' option for the Service Desk Agents. Is there a way to add this for other users? This is an internal employee and has an account on the system for other projects.
Also, they required to be able to see all of those tickets and their status. Is there a way to expose those in the portal? or will they need to login to the project? I'm ok with them logging in to the project to do all of this, as it would be easier to set 'reporter' and 'watchers'. The only problem is I can't see an option to disallow them from seeing other teams issues.