How do I flirt with him without other girls understanding what I am doing?

Well, there is this guy that EVERY single girl is in LOVE with. Well, I keep telling him he is a jerk in a joking way and I love teasing with him. He is in my homeroom, Reading, and Science cles. Well, deep down inside, I don't think he is a jerk. I actually think he is pretty nice. I really want to flirt with him, but if I do, than other girls will get mad at me because I told every one that I don't like him. So how do I flirt with him without other girls understanding that's what I'm doing? And that he will get the idea that I'm flirting. He isn't the kind of guy that would blurt out, "You're flirting with me!!".