In a bowl, sprinkle the strawberries with sugar; stir to distribute the sugar, and set aside. Chill a large metal mixing bowl and beaters from an electric mixer.
Pour the cream into the chilled mixing bowl, and add pudding mix, lemon yogurt, and about 1 tablespoon of coconut rum, if desired; beat until fluffy with an electric mixer set on Medium speed.
Spread a layer of pound cake cubes into the bottom of a glass 10x15-inch baking dish, and sprinkle the cubes with another tablespoon of coconut rum. Cover the pound cake with a layer of strawberries; sprinkle blueberries over the strawberries. Spread a thick layer of whipped cream over the berries. Repeat the layers several times, ending with a layer of strawberries sprinkled with blueberries and reserving about 1 cup of whipped cream; top the trifle with dollops of whipped cream to serve. Refrigerate leftovers.