SK, as you know I am a big letter writer so I recommend he write a letter to the CEO of Sprint.
It's easy to find out whom that is. Just go to their site and scroll to the bottom and click on "Investor Relations." Once into that field click on "Company Officers." He/she would be listed there.
Keep the letter to one page and be as clear as possible. Cover in this order:
1) What happened
2) When this happened
3) What you expect from the CEO/Sprint for the inconvenience caused by the Sprint employee
- Apology letter
- A tank of free gas (Reasonable)
Send it via snail mail and if your friend does not receive a response within 10 business days post the letter on his and their FB page.
Good luck!