If the champagne is dry or sec, you can use it for a sauce for poached salmon :
Saute shalots in a little butter, add champagne and reduce, add heavy cream and reduce. Adjust taste with a hint of Tabasco and a dash of lemon,
Sauce may be thickened with a little maizenna in a drop of champagne, or with an egg-yolk.

If you make a soup, from mashed peas boiled with thyme, sage and onion in stock, you can add champagne in stead of sherry just before serving, preferably with a dollop of whipped cream in plate while serving.

If the champagne is sweet or sweetish, I would have used it in a champagne sorbet with whipped egg-whites.

Luxury problems are also problems!!