Single Theme folder for Multiple WordPress

I ran into a scenario where I want to achieve this.

WordPress Site 1
WordPress Site 2
WordPress Site 3
WordPress Site 4

I want theses four sites to have a single theme folder and it get themes and run themes from there not from

WpSite1/wp-content/themes
WpSite2/wp-content/themes
and so on

Thanks

WP inherently supports multiple theme directories via register_theme_directory().

However since it requires web–accessible directory you might have to symlink or otherwise muck with it server–side so that all sites pick it up. Up to your configuration how to do it exactly.