What is the best way to attach stones to a cinder block wall that has mortar/plaster on the outside?

We have a cinder block wall (20' x 4') where the mortar is crumbling off the face. We wanted to attach some stones to the outside just for looks but don't want to scrape all the mortar off. What can we use to put over the plaster so the stones will stick. We are thinking some type of wire and screws but not sure how or what we should do. Thanks.