In a large bowl or a stand mixer fitted with the whisk, combine 1½ cups cream, mascarpone, pumpkin, sugar, 1/2 cup sweetener, and pumpkin spice. Beat on high speed with a hand mixer or medium-high speed in stand mixer until stiffly whipped.
In a medium bowl beat remaining ½ cup heavy cream with 1 tablespoon sweetener until stiffly whipped.
In a small bowl stir together coffee, rum, and remaining 1 tablespoon sweetener.
Have ready 6 approximately 4” wide cups or ramekins. Dip ladyfingers in coffee mixture and line cups or ramekins with a single layer (depending on size of cups or ramekins, ladyfingers may need to be cut shorter with a serrated knife).
Top with a layer of pumpkin mixture. Top with another layer of soaked ladyfingers and another layer of pumpkin mixture.
Top each serving with a generous spoonful of whipped cream and sprinkle with white chocolate. Serve immediately or refrigerate, covered, up to 1 day.