You’re getting great advice here, but I’d add one more thing you could do to help your friend without putting your job in jeopardy: Tell him he should look into a legal term called Quantum Meruit and bring it up in Small Claims Court. It’s a concept that says he should get fair value for his work, even if there’s not a formal contract. Of course, he still has to show that your boss asked him to do the work, and a Small Claims judge might decide he’s not entitled to such a high hourly rate, but I bet that gets him something.
Disclosure: I’m the CEO of Freelance Collection. We help freelancers and small businesses get paid when clients try to skip out on the bill. Also, I’m not a lawyer, so don’t take this as legal advice.