Choose some guys who are respected by their peers. These guys have to possess some positive leadership qualities. Call the parents of these young men and request an interview with the student in the presence of their parents in their home. Tell them who you are and that you would like a few minutes of their time to discuss your program with them. Tell the young men you need their help.
Many students like to feel that they are helping do something for their school and community.
Present everything as honestly and positively as you can. Play this honest with the kids from the beginning. I've done this several times in my career spanning 20 years. If I'm successful in getting the parents and student to sit down with me and discuss my goals for music in the school, I've gotten the young man to enroll in choir. My High school choir has 13 girls and 1 boy in it.