I learned this masked spritzing technique at the Stampin' up! Regional Seminar in November. Watch my blog for a video to be posted this weekend! (Will try to remember to update with a link).
Basically -- die cut the snowflakes with cardboard. Set them on cardstock and use the Stampin' Spritzer with rubbing alcohol and reinker. Remove the cardboard shapes. Allow to dry. (I stamped the snowflakes first. It was easier to line up the die cut shapes over the stamped image than vice versa.)