In medium saucepan, combine first 5 ingredients; bring to a boil over high heat. Boil until thick and syrupy (about 5 min.); cool to room temperature. Marinate peach halves in glaze up to 1 hr.
To Grill: Using direct heat cooking method, preheat grill to MEDIUM-HIGH. Grill peaches, covered, cut-side-down until lightly charred (2-3 min.); turn and brush with additional glaze. Continue grilling, covered, until peaches are soft (about 5 min.). Remove from grill and arrange on individual dessert plates. Divide mascarpone evenly among peaches; drizzle with honey and garnish with mint. Serve immediately.