Got a couple of ideas: take all the literature, I mean keep doing it, every week be there as soon as they get there to set up and just scoop up the whole lot... And when they eventually try to start a bible study explain that you love their publications because they make such great cat litter liners!
Or make up ways to spill stuff "accidentally" all over the cart and literature. Like coffee, or ketchup from a bottle, baby bottles full of milk squirted. Etc etc
Or... Hit them at the source donate to the bored and cold jw's there some free coffee that you've brought them.... Just slip some high strength laxative into it first!!!