You can use the meal plan for breakfast. If it is a buffet, or sit down restaurant, it will use a TS. There are CS breakfasts, but you have to look for them. In MK, the only CS breakfast listed is the Main St Bakery. Epcot has Fountainview Espresso Bakery and Sunshine Seasons for CS breakfasts. The All Star Resorts have CS breakfasts offered at their food court...that is probably the best bet if you are staying there.
To find the CS breakfasts, take a look here:
http://adisneyworld.disney.go.com/m...gespecific/eng/nontheme/tickets/MYWDining.pdf
Breakfast is usually the cheapest of the meals, so you don't get as much value by using CS for breakfast and not lunch, but the whole point of the plan is for flexibility so it should work for you.