If the pastor has a relationship with the man he would be the best one to talk to him.
He may want his child to grow up to walk with Jesus even though he himself does not want to do so. He could choose to stand there as a support to his wife and not speak, or choose to sit in the audience and observe. Give him the choice. (These are just thoughts, not sure how confident I am with them :) )
I train churches to develop after school ministries. A Buddhist mom brought her son, an elementary child, to sign up for the ministry.
Director: If your son comes here he will be taught to be a follower of Jesus.
Mom: Good, good
Director: But you are a Buddhist, why would you want him to be a follower of Jesus?
Mom: Because then he will be a good boy.
May God show you what He wants you to do, may He open and close the doors.
Do you require a class or any requirements leading up to the ceremony? Everyone has to attend a class with out where we talk about what this moment means. We've never had anyone pull out, but it does give us the ability afterwards to approach parents if they aren't living up to their commitment. Have the Sr. talk to him about the commitment that the child dedication will require. Maybe this will be the one that changes his heart.