Sometimes I will roll into a town late (too late to spend too much time looking for a campsite) and I always look for an apartment complex. There are usually flat, empty spaces next to the buildings.
If someone asks what you're doing, tell them you're "testing my camping equipment." They'll assume you live in one of the apartments. As long as you're gone early, no one will bother you and it's doubtful you'll run into the manager.
It's not ideal (traffic, loud "neighbors") but finding an apartment complex will work in a pinch. And as long as you're not building a bonfire, the cops will leave you alone, too.