Make gingerbread: Preheat oven to 350 degrees F. Line a buttered jelly-roll pan, 15 1/2 x 10 1/2 x 1-inch, with wax paper. Butter and flour paper, knocking out excess flour.
In a bowl whisk together flour, baking soda, salt and spices. In a large bowl with an electric mixer beat together butter, sugar, molasses, and oil until combined well. Beat in eggs, 1 at a time, beating well after each addition, and add flour mixture, beating until batter is combined well.
Spread batter evenly into prepared pan and bake in middle of oven 15 minutes, or until gingerbread springs back when pressed lightly. Invert gingerbread onto a rack and cool completely. Peel off wax paper. Gingerbread may be made 1 day ahead and kept wrapped in plastic wrap. Cut gingerbread into 1/2-inch cubes.
Make blueberry sauce: In a small saucepan simmer sauce ingredients, stirring occasionally, 40 to 45 minutes, or until reduced to about 2 1/2 cups. Cool sauce completely and chill, covered. Blueberry sauce may be made 2 days ahead and chilled, covered.
Make lemon mousse: In a heavy saucepan whisk together yolks and sugar. Add lemon juice and butter and cook over moderately low heat, whisking constantly, until butter is melted completely. Cook mixture, whisking constantly, until it just reaches the boiling point and is thickened (do not let mixture boil), 7 to 12 minutes more.
Strain lemon mixture through a fine sieve into a bowl. Stir in zest and cool mixture completely, its surface covered with plastic wrap. Chill mixture until cold, about 2 hours.In a bowl with an electric mixer beat cream until it just holds stiff peaks. Whisk one-fourth whipped cream into lemon mixture to lighten it and fold in remaining cream gently but thoroughly. Chill mousse, covered, at least 3 hours or overnight. Mousse may be made 2 days ahead and chilled, covered.
Arrange 1/2 cup gingerbread cubes in bottom of each of 8 glasses (about 1 1/2 cup capacities). Spoon 1/4 cup mousse over gingerbread in each glass and spoon 2 heaping tablespoons sauce over each layer of mousse. Repeat layering with all but about 1 cup gingerbread and remaining mousse and blueberry sauce. Alternatively, a large trifle can be made in a 3-quart bowl by layering ingredients in same order.
Chill trifle, covered, at least 6 hours or overnight. Garnish trifle with zest.