Toss banana slices with lemon juice; drain off excess. Set aside 6 banana slices for garnish; divide remaining slices evenly among six lightly buttered 6-ounce custard cups. Set cups in shallow baking pan.
Beat eggs, milk, granulated sugar and rum extract until well blended; pour evenly into custard cups. Place pan in preheated 350°. oven; pour VERY hot water into pan to within 1/2 inch of top of cups. Bake about 40 to 50 minutes, until knife inserted near center comes out clean. Remove cups immediately from hot water; cool on wire rack 5 to 10 minutes.
To serve, gently loosen custards with thin spatula; invert onto serving plates and garnish with reserved banana slices. Melt butter in small saucepan over low heat; blend in brown sugar, water and cinnamon. Bring to a boil; boil 3 minutes. Spoon about 1 tablespoon hot syrup over each custard and serve immediately. Serves 4.