I did read in one of the Tracy's books, that you can make a small cut into the teat of the bottle, so that the milk flow increases, then a few days later make another cut, until after a while you have made four incisions which end up in the shape of a cross. She said that they lose interest then. I tried using soft beaker teats which fit onto bottles (from mothercare). Eventually I think it was just gradual persistence of offering a beaker which did it for us.