Take a key or a coin and hold it comfortably using the fingers closer to the thumb. Stand at a comfortable distance from your partner and move your hand outside of his line of sight and pinch the back of his neck or the lower part of his arm (just a suggestion) between the object and your thumb. Now you have to avoid stopping and gripping him because in this way you are simply anchoring yourself and stopping yourself so the pinch needs to be simply a part of the moving hand and you use it to guide and control your partner toward what is safer for you. Work on this from different positions such as when being chocked or from a seat of a car (keys are usually used in a car) and remember that the pinch is just a distraction and concentrating him at one point so the rest of him is free for you to control. Avoid focusing on your pinch and just keep moving and if this does not work try something else. As long as you are breathing there is hope.
Consider pinching without an object as well and remember it is just a tool.