In a saucepan over medium heat, stir the white sugar and water until the sugar has dissolved and the mixture is boiling. Remove from heat, and let cool completely. Pour the syrup into a large mixing bowl, and beat in vegetable oil, shortening, and clear vanilla extract with an electric mixer on high speed to blend.
Beat in the confectioners' sugar, 1 cup at a time, until the filling is thick and fluffy. If it's too thick, beat in a tablespoon of water at a time until it's the correct consistency.