Add "don't publish" tick to my facebook app

HI, I have a facebook app which simply needs to have and "don't publish to friends wall" option which would be ticked (selected) by users if they don't want to publish their answer to friends wall (which actually does). So the task is: Add option that user will click or tick to prevent wall posting for that action. the app is this: [login to view URL] Facebook developers will understand immediately what i am talking about ! Florim