You need to provide a lever on the coupling, either the coupler shaft itself between coupler knuckle and the pivot point or add a lever after the pivot point if you have enough room.
Then you need to provide a motivate means to each side of the lever, like two weak springs or two pieces of elastic cord. They should be attached to the lever and to two anchor points one on each side of the lever.
You might also use one thin piece of weak flexible springy metal as the new lever and provide a limiter on each side of the lever to provide the anchor while letting the lever move lengthwise.
There is not a single solution that will work on every coupler. You will get to be innovative and creative.
I have had some success adding two pieces of elastic cord on each side of the coupler shaft on a switcher engine. Examine the front coupling of your switcher engines, if you have any, for examples
Charlie
