This capability is not possible in Portal for ArcGIS. May I suggest a different approach: instead of pre-loading favorite maps/items to all of your Portal members' profiles, why not leverage the Gallery option in Portal?
Take all of the items that you want to promote as favorites and place them in a group. Then assign that group to the "My Organization's Feature Content" tab on the Gallery page.
To enable: My Organization > Edit Settings > Gallery > select the group.
Then simply direct your Portal members to go to the "My Organization's Feature Content" tab on the Gallery page.
Hope this helps,