This is the perfect project! And pretty too!
Mix about a teaspoon of the gesso/paint in 1-2 tablespoons of water. It shouldn't be too evenly mixed; if it's a wee bit lumpy that just adds to the snowy-ness of the mix.
Leave to dry and that's it. Place on tea-light holders so they balance on the rim. Of course you won't put a tea light inside the holder, m'kay! Or fill a bowl with your sparkly cones. They will also be a lovely, simple decoration on your table.