Melt margarine in a large nonstick skillet over medium-high heat. Add minced garlic, and sauté 2 minutes. Add roast beef and next 6 ingredients (roast beef through beer), and bring to a boil. Reduce heat, and simmer 2 minutes, stirring frequently. Drain roast beef in a colander over a bowl, reserving sauce. Divide roast beef evenly among roll bottoms, and top with roll tops. Serve sandwiches with reserved sauce. Garnish sandwiches with carrot curls and olives, if desired.