Add between a dash and a teaspoon, to taste, of absinthe to Calvados, lemon, and sweetener, shake with ice, and strain into a highball over ice and Champagne (or, more festively, into a Champagne flute over bubbles).
Other sweeteners work well: grenadine, of course, Pommeau de Normandie, and so on. You could also add a dash of Angostura, which always works well with absinthe, or douse a sugar cube in bitters, as in the Champagne Cocktail and Jimmie Roosevelt.
I thought about how the French 75 memorialized the artillery of choice during the first World War, and how absinthe, then banned, was used in the production of gunpowder during that war. (See source reference.) From there it was a trip to Normandy, thirty years later, via Pan American Clipper.