Redmine

Hi,
I have nice quest. So here is example.

1) I have private project, because I need to see this only members.
2) I add issue, I'm member of this project.
3) BUT I need to add my friend as watcher or assignee, because this issue hit his work too, but my friend isn't member.

RESULT?
I CAN add him as watcher, but he DOESN'T see project or issue and he isn't notified.
I CAN'T add him as assignee, because he isn't member.

POSSIBLE SOLUTION?
Add him as member to the private project. But I don't want to do this everytime when I need him to watch the issue/s.

QUESTION:
If my friend add as Watcher, can he reach temporaly permission like user-member?

HOW I THINK ABOUT IT?
1) I have private project, because I need to see this only members
2) I add issue, I'm member of this project.
3) I add non-member users as watcher.

AFTER ADDING
- non-member user can see project in list of projects
- non-member user can see issue from private project, where is watcher
- non-member can add comment, etc. issue from private project, where is watcher (temporary permission like member with "User" rights)

WHY?
I have around 30 projects, all public. Almost everytime I need to get issue from one project to another, like from POOL to SW HELP and I need to keep user access to his issue.