Combine rice, 2 cups milk, vanilla, ginger, and orange peel in saucepan; bring to boil. Reduce heat to medium low; simmer, stirring, until liquid is absorbed, about 12 minutes.
Stir in cream and remaining 1 cup milk. Cook over medium-high heat, stirring frequently, until rice is tender, about 10 minutes. Remove from heat; remove and discard the ginger, vanilla bean, and orange peel. Stir in sugar; let stand 2 minutes. Stir in mascarpone and macadamia nuts; let stand to cool slightly. Divide among 12 small serving vessels. Garnish with macadamia-nut topping. Serve warm or at room temperature.