In a large saucepan, combine gelatin, milk, egg yolks, granulated sugar substitute, salt, and cocoa.
Cook over medium heat until completely blended and slightly thickened.
Remove from heat.
Stir in rum extract and refrigerate until partially set.
In a small bowl, beat egg whites with liquid sugar substitute until stiff peaks form.
Fold into cooled chocolate mixture.
Layer the chocolate mixture and whipped topping in the pie shell, ending with whipped topping.
Refrigerate for 2 to 3 hours or until firm.