Combine the quartered plum, lemon juice, and ginger in the medium bowl. Add ¼ cup light brown sugar, 1/16 teaspoon salt, and 2 teaspoons cornstarch. Toss it all together, then divide among the prepared ramekins. Place the ramekins on the foil-lined baking sheet.
In the bowl of the food processor, add the whole wheat pastry flour, the remaining light brown sugar, remaining 1/16 teaspoon salt, and the baking powder. Pulse 3 times. Add the butter, lemon zest, and cream cheese, and pulse until the mixture resembles coarse meal. Add the buttermilk and pulse a few more times until blended.
Drop dough by spoonfuls over the plum mixture, and sprinkle the biscuit tops with the raw sugar. Bake in the preheated oven until the biscuits are golden and the filling bubbly, about 30 to 35 minutes. Allow to cool and serve warm or at room temperature.