The prodigal's brother

When I preach on the parable of the prodigal son, I always get stuck on the elder brother. I wish there were a fifth gospel in the New Testament devoted to reaching out to that guy because he's everywhere in the congregation I serve, wearing many names and faces. Frankly, we depend on elder brothers to keep the place running. But I struggle to know how care for them.
I've tried giving elder brothers more stuff to do because they happily accept, and I've tried encouraging them to work to create a more just society because I know they think it's up to them to get things right. But both of these strategies miss the point of this parable—and the gospel of grace.
Most preachers know how to proclaim grace to the prodigals. "It's OK," we keep saying, "God knows what you have done, but you are forgiven. All you need to do is come home and accept the forgiveness that is waiting for you." We can make those words sing for those who have screwed up their lives, but what does the gospel say to the elder brother who spends his life playing by the rules?