Routledge was allowed to leave Newcastle last year, 19 months into a 3½-year deal.
Graham said: "Wayne has had a superb season for us and it's up to him to go back up there and show them what they are missing.
"I'm sure Wayne wants to go back and prove a point.
"Newcastle wanted rid of him and that was why he came here.
"But I always joke to Wayne that he has lived my dream of playing for Newcastle."