My question would be, "Why are you running it through your insurance?"
Your "friend" should run it through his insurance. Then he can pay any deductibles, insurance increases, etc. Why should you have to pay anything?
The only people I have even offered to let drive my Viper is my wife and daughter. When I asked, I was pretty confident they would decline, and they did, because they knew how I felt about my "baby". If they had actually taken me up on my offer I don't know what I would have
done, but I would have thought of something. Really I had to offer to my wife. She's on the title with me. That was done so that when I pass away, (because I'm sure I'll have it that long) she will own it and can sell it without it have to go through probate.