How should my friend tell a guy she doesn't like him without hurting his feelings?

I'm a guy asking for advice for a girl. Here it goes. My friend-girl and I walk with each other after school everyday. We've recently begun having another guy walk with us. He's our friend but her and I like to walk alone. This guy that walks with us likes her also. She doesn't like him and she wants to tell him but doesn't want to hurt his feelings. To summarize in two questions, how does she tell him she wants to walk with me alone? And, how does she tell him she doesn't like him but still wants to be friends?How should my friend tell a guy she doesn't like him without hurting his feelings?
There isn't really any way to avoid hurting this guy's feelings. Rejection, no matter how nice you are about it, always hurts. Just be open and honest about it, yet be tactful. Let him know that you don't want to hurt him and you do want to be friends, but you and this girl would like to be alone when you walk home.