I found this on the Splenda website, and while not completely legal, I'm doing a lot of baking again this Christmas and intend to use this as a better-than-the-alternative substitute.

"Powdered Sugar Glaze"

Preparation Time 10 min.
Makes1/3 cup glaze

1 1/2 cups SPLENDA? Granular
1/4 cup Cornstarch
5-6 tsp. Water

Place SPLENDA? and cornstarch in blender jar. Cover and blend until SPLENDA? is a very fine powder. Pour into a small bowl. Add water and stir well. This recipe makes a thick glaze. Add more water for a thinner glaze.

To flavor the glaze add any of the following; 1/2 tsp. vanilla extract, 1 drop maple flavor, 1 tsp. lemon zest, 1 tsp. orange zest, or 1/2 tsp. rum flavor.

Nutrition Information per serving
(1 Tbsp.)

Total Calories 45
Calories from Fat 0
Total Fat 0 g
Saturated Fat 0 g
Cholesterol 0 mg
Sodium 0 mg
Total Carbohydrate 11 g
Dietary Fiber 0 g
Sugars 0 g
Protein 0 g

Exchanges Per Serving
1/2 carbohydrate