If you're such close friends, as it really seems that you are, then just tell him. I have a friend similar to yours. We've been friends since 5th grade and might as well be brothers. If I was faced with such a predicament I'd just say "Dude, you golf like old people f***. I love getting out on the course with you, but if you don't speed it up I'm going to slash your tires when we get back to the parking lot."
Now obviously your choice of words doesn't need to be the same as mine, but when you've been such close friends with someone for so long, through thick and thin and sharing all kinds of crap together, you're friendship is clearly strong enough to survive such a truly minor hiccup in the grand scheme of things.