I've heard of someone this forum who went down the street in their neighborhood after the Witnesses had stopped by and did "anti-Witnessing". They told their neighbors the other side of the JW story.
I suppose if you or several people had the time, you could wait outside the Hall and quietly follow a car group(s) into a neighborhood(s) and quietly follow behind them from door to door leaving anti JW literatrure. The thing is, the door to door work is barely effective in itself so there's probably no need to spend any time trying to undo their efforts. But it would startle or embarrass JW's if they knew there was such an organized effort going on to warn people about them. Just to be prepared, they might even look into what is being said about them which could start some of the long ignored wheels turning in their heads.