Add sugar, soymilk, and cornstarch to a small saucepan off of the heat. Stir until lumps of cornstarch disappear. Turn on heat to medium high and bring to boil, stirring constantly. Boil until thickened.
Remove from heat and allow to cool to room temperature.
Whisk in lemon oil, lemon juice and margarine until smooth and creamy. Spoon or pipe into desired baked good. Excellent in cream puffs, this should be great in cupcakes or as a cake filling.