Adjust oven rack to lowest position and heat oven to 400 degrees. Place potatoes, cut side down, on an oiled parchment-lined baking sheet. Bake until fork tender, about 30 minutes; let rest until cool enough to handle. Working one at a time, hold potato half in one hand and scoop warm potato flesh into a blender, leaving enough flesh behind to create a sturdy shell. Add butter and creamer; puree, stopping and stirring, if necessary, until creamy smooth. Spoon puree back into shells, top with pumpkin seeds and return to oven. Bake until heated through, 10 to 12 minutes. Serve.