You can add user's as contributors by going to the "Admins" tab on the edit page. By default, the contributor will not have the game appear on their profile page. The easiest for them to add it would be to add it to a collection and put that collection on their page
Edit July 2018
You can add someone as a contributor to your project then they'll be able to add the game directly to their profile from their profile theme editor. It's no longer necessary to use a collection.