How to make The Jello Shots Cocktail. In a medium bowl, stir together the Jell-O and boiling water until the Jell-O dissolves. Add the vodka or rum and cold water, and stir to combine.Pour 1 ounce of the mixture into each of 16 shot glasses (small plastic or paper cups will also work) and chill until solid.dd the vodka or rum and cold water, and stir to combine. Pour 1 ounce of the mixture into each of 16 shot glasses (small plastic or paper cups will also work) and chill until solid.