Melt margarine in a large, non-stick skillet and saute carrot and onion until soft. Add rice and continue cooking until golden brown. Add broth, cover and simmer until rice is tender – about 20 minutes. Meanwhile, squeeze excess liquid from spinach. Add to cooked rice, along with seasoning.
In a large bowl, with mixer on low, beat egg substitutes for I minute. Add milk and salt and continue to beat. With motor still running, add melted margarine a little at a time. Lightly coat the bottom and sides of a double boiler with margarine, and place over barely boiling water. Pour in egg substitute mixture. Cover and cook at low temperature for ten minutes. Turn the congealed portion of the egg substitute mix from the sides to the middle. Cover and continue cooking for 5 minutes longer, or until firm. They can be kept warm over hot water for up to 20 minutes.
The day before serving, bake potatoes in a 450-degree oven until tender. When cool enough to handle, split in half and gently scoop out flesh. In a medium bowl, coarsely mash potatoes and combine with the next 4 ingredients. Brush insides of potato shells with melted margarine and divide filling evenly among the 8 shells. Cover and refrigerate overnight. About 10 minutes before serving, re-heat in a 350-degree oven or in microwave until cheeses melt. Serve with sour cream.