To prepare cakes: Preheat the oven to 350 degrees. Lightly mist 12 (4-inch) tube pans with nonstick spray; dust with flour. Shake out excess flour. Set pans aside.
Place white chocolate in a small glass bowl; microwave on medium (50 percent) power until almost melted, stirring every 30 seconds with a small rubber spatula, then stir until smooth. Let cool slightly.
Combine cake mix, lemon zest, oil, water, eggs, lemon juice and melted white chocolate in a large mixing bowl. Beat with an electric mixer on low speed for 1 minute. Scrape down the sides of the bowl with a rubber spatula. Beat on medium speed for 2 minutes, until well combined. Spoon batter into prepared pans, filling each 2/3 full.
Place pans on the center oven rack. Bake cakes until they spring back when lightly pressed with your finger, 20 to 25 minutes. Let cool on a wire rack for 10 minutes. Run a sharp knife around edge of each cake; invert onto a rack. Invert again and let cool completely, 20 minutes.
Meanwhile, prepare lemon drizzle: Sift sugar into a small mixing bowl. Whisk in enough lemon juice to make the glaze smooth and easy to spoon. Fold in zest.
Spoon drizzle over each cake, allowing it to run down the middle and sides. Let cakes rest for 20 minutes before serving.