In a medium bowl, using a rubber spatula, toss the gelatin mix with the cake pieces; set aside.
Using an electric mixer, beat 2 1/2 cups cream just until soft peaks form. Put a heaping tablespoon of cream in each of 12 juice glasses or tumblers. Top with 3 cake cubes. Spoon another heaping tablespoon of cream over the cake and top with 3 more cake cubes. Repeat the layering, ending with cake, until the glasses are filled. Transfer to a rimmed baking sheet, cover with plastic wrap and refrigerate at least 6 hours or overnight.
Just before serving, beat the remaining 1 1/2 cups cream until soft peaks form. Fold in the lemon peel, then spoon onto each dessert.