Rhino 7.17 (currently in release candidate) will load packages from both %AppData%\McNeel\Rhinoceros\packages\7.0\ and C:\ProgramData\McNeel\Rhinoceros\packages\7.0.
However there isn’t currently a way to install packages directly to the second (“All Users”) location. You’ll need to install them normally and then copy them across from the AppData packages directory (making sure all users have access to the files).