this might be a uk thing is that right? its about inviting people to come to church who havent been for a while for whatever reason.
we did it last yr and used songs like come now is the time as it says the line, 'come just as you are to worship'. this is the essence of back to church sunday as i understand it.
i would encourage you to make sure the whole service is welcoming and accepting. songs about the prodigal son are good also. like 'prodigal' by steve parsons for example. www.steveparsons.net