Line a 9-by-13-inch baking dish with foil, leaving a 2-inch overhang; coat with cooking spray. Melt 4 tablespoons butter in a large pot over low heat. Stir in 10 ounces mini marshmallows until melted and smooth. Stir in 1 tablespoon each grated lemon zest and lemon juice and 1/2 teaspoon vanilla. Off the heat, stir in 6 cups crisp rice cereal, 12 crushed Lemonades and 1/2 cup white chocolate chips. Press the mixture into the pan and let set. Cut into pieces.