Take a blade screwdriver with a blade end width of at least 8mm and heat it to red with a gas torch. Press it into the centre of the offending cleat until you make a reasonably deep slot in the plastic, but DO NOT move the blade end about during this, the slot needs to be as snug as possible a fit for stage 2. Cool the blade off with water until its properly cold and also cool off the cleat with a few splashes of water, now use the screwdriver as normal and twist the cleat out. The much greater leverage afforded by the length of the screwdriver shaft should make it easier that using the standard cleat tool. Obviously this all depends on how much of the body of the cleat remains, you usually need to make the slot around 3mm deep to get good enough purchase. Using a nice stout thickness of screwdriver blade also helps.