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.
Peach-and-Mint Ice Mold:
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.