This is just me-- but since almost all of my points were earned on work trips and I didn't pay for them myself, I would have a hard time charging my friend for them. I've used points countless times on football trips when we are only out 1-2 nights, and I've never charged anyone else for them. I've done this with car rentals as well.

You can tell him to buy you a couple of meals, take care of some gas if you rent a car, etc. Still, it doesn't hurt to share your generosity with others. Just my opinion. I consider myself very blessed to have these travel opportunities and I love the fact that sometimes others get to share my good fortune. It keeps karma in my favor.