No, there really is no accepted therapy to address motor or vocal tics. As you know, by definition tics are involunatry movements. While they can be exacerbated by stress, they are not actually caused by stress. You have done the reasonable things to investigate your son's condition. On a positive note, over time such tics do tend to wane. Now, there are some medicines that can be employed if the tic is a major interference with normal social functioning. Your neurologist can help you consider the options. But I would be irresponsible if I suggested to you that psychotherapy will help your son. Supportive therapy can be useful if the child feels stigmatized or ostracized by the tic and its impact in relationships or peer approval/acceptance, but the therapy would not be directed toward stopping the tic.