Place the peach-and-mint ice mold in a large punch bowl. Add the vodka, creme de cassis, peach syrup, lime juice and champagne. To serve, ladle into glasses over ice.
Place the peaches and mint in the bottom of a 10- to 12-cup Bundt pan, and fill with cold water to about 1 inch from the top. Freeze until set, about 24 hours.
To unmold, let sit at room temperature for about 10 minutes, or dip pan in a warm water bath for 10 to 20 seconds, then invert.
Place the peaches, sugar and 2 cups water in a medium saucepan over medium-high heat. Bring to a simmer, and cook until the sugar dissolves and the peaches have softened, 8 to 10 minutes. Transfer to a blender; blend until smooth. Refrigerate until ready to use.