Combine 1/4 cup juice and peel in small saucepan; sprinkle gelatin over. Let stand 5 minutes. Add 1/4 cup cream to gelatin mixture; stir over low heat just until gelatin dissolves. Remove from heat.
Whisk mascarpone and 1/2 cup sugar in medium bowl; gradually whisk in remaining 1 cup cream until smooth. Whisk gelatin mixture into cream mixture. Pour into 6 widemouthed Champagne glasses or small wineglasses. Chill until set, at least 4 hours or overnight.
Stir remaining 2 tablespoons lime juice, 1/4 cup sugar, and butter in large skillet over medium-high heat until sugar dissolves, about 3 minutes. Cool 2 minutes. Fold in berries; spoon over desserts. Grate peel from 1 lime directly over desserts.