I don't know how fancy it has to be, but what I used to do in school was cut strips of paper and fold them like an accordian fold. Then glue (or tape) one end of the paper to the thing that had to pop up and the other to the page in the book. Don't make the paper too long or else it will hang down. Don't know how much help that is, but you could try it. Maybe someone else will have a more professional looking idea.