The best method I've found in dealing with tailgaters is to gently "wave" them back. Extend the left arm with the hand toward the ground and slowly move it as if you are pushing them back. If they back off, give them the thumbs up signal to thank them. If they don't, find a good place to let them by. It may be hard to use a gentle wave and avoid the other rigid digit sign when they are extremely close, but keep your cool. Folks respond better to requests, which is what the gentle wave is, than demands, and leaves a better impression of bikers. Plus, you are educating them for other bikers.