I don't believe that this can be done. However once you add people as friends and then add them to your mob, you can delete them from your friends list and they will remain part of your mob. If you want to do a test just look at the number of mobsters that you have. Then delete one friend. When you go back to look at the number of mobsters that you have, the number should be the same number it was before you have deleted the person from your friends list. Any other way just such as downloading a program is cheating and your leaving yourself open to have your computer hacked.