Best course of action to take when confronted by an overly enthusiastic well wisher?

Oh you know the kind. Or maybe you don’t, I dunno. A friend of a friend or maybe distant family member who, upon hearing of your good fortune or a well earned piece of good news just over does the back slapping & so on a little too much. Can’t get rid of them like a leech they’re stuck there. All attempts at courteous removal have fallen on deaf ears. What to do that wouldn’t cause too much offence? This has happened to me on more than one occasion, I must be a soft touch. I normally give a knowing glance to a friend who distracts/removes the offender while I stealthily make good my escape.