Pretty sure it's already like that if you have inheritance/targeting set up right.
Have owner inherit from co-owner, co-owner inherit from superadmin, superadmin inherit from admin, admin inherit from moderator, and so on. Then just have each rank be able to target only their ranks and ranks below them, you can do this as follows:
Moderator be able to target "%admin", admin able to target "%superadmin" and so on. If this doesn't work for you then you might have a different addon that handles players picking up players, or I might be forgetting how physgunplayers works. I hope this helped you.