http://www.vasst.com/resource.aspx?id=0136efd8-c125-4388-b63a-4108bb1bde6c will show you exactly how to achieve it with generated media. You'd likely want to keyframe in the movement of the person, or, create a Bezier mask that hides a specific area of the text so that when your subject moves, the mask moves with the subject, revealing the text.