If you lightly flour your hands and the dough ball around the edges, you can hold the container upside down and gently pry it away from the sides and then towards the center. As gravity works on the dough mass, be ready when it drops - right into your floured hand. Then flip onto your board.
You can also get a larger container, like a tray, and then use a dough "knife" to remove the balls. Usually a dough proofing tray is dusted with flour instead of oiled. The tray scenario also gives you some room to work, as opposed to the straight sides of a small tupperware.