link/tab that allows a visitor to return to the main site?

I have been searching for a multi-site plug-in that inserts a link/tab into navigation of all sites within a multi-site WordPress (except the main site) to allow a visitor to return back to the main site (like a ‘home’ button for the entire network).

I am very surprised that I can’t find that ability anywhere, do any of your plug-ins for multi-site do this? If not would anyone consider creating such a plug-in?