I say eat as much as you want. You may want to try millet.
I never transitioned at all. While it could work it tends make things more difficult.
It depends on how many calories you need to catch up on. If you've eaten 1600 calories from fruit, you might be able to get away with eating 1-2 400 calorie servings of rice and be sufficiently carbed up. But you'd be better off going for more bananas or something at that point.