Not to rain on your parade, but even a letter is very unlikely to help. USNA asks for the LORs it wants. It permits
(does not encourage) additional letters because there are situations where the mandated recommenders may be unaware of a key
aspect of the candidate's life. Some examples: (1) the candidate has to work after school and on WEs to support his/her family so a letter from the employer would be very helpful; (2) all of the candidate's activities occur outside of school (e.g., church, scouting) so a letter from a leader of one of those activities would be helpful.
Letters from family friends who will say some version of the following: great human being, wanted to go to USNA since a baby, committed to service, strong leader, exceptional athlete, blah, blah blah -- will almost certainly not
be helpful. Now, if your family friend is the President or Vice President of the United States . . . probably a different story.