Your case is little different. Ideally, my approach would be to get his insurance info and call them and have them pay for everything. Since you said he was involved in dui he's already at fault. So what you could do us call your insurance company and tell them that you ere involved in an accident and you need a rental car. You could tell them that he was charged with duo to enforce that he was at-fault party. Again dealing deal with insurance companies is pain, I hope you have full coverage and a good insurance company. Don't rent it from your fren since its not reimbursable for the insurance company. Ideally I wouldn't involve my company on all of it, but in your situation its not viable.