Normally I am dead-set against putting other liquors, flavors, or liquids of any kind in Champagne. Why would you want to do that to your fine Champers?!?! Use Prosecco or any non-Champers French sparkler, or Cava. Having said that, however, I was at the Ritz-Carlton and they had a Champagne cocktail (using Louis Roederer champers) flavored with this Kiwi syrup made by Monin. It gave my champers this surreal, absinthe-like, glow and it was delicious. Google Monin and kiwi and you’ll find it.