Save that for later. The innocent act will turn him on even more. Reach your hand in, slide his pre-cum down his shaft, and start giving him a proper hand job. Start with your shirt.
When you have sex with a man, watching them experience an intense orgasm is pretty rewarding. Helping a man have a mind-blowing orgasm is not as easy as it looks. The great thing about making someone have an insane orgasm is that they want you to experience that feeling as well.