Add sugar water and ginger to a small saucepan and heat over medium heat until sugar dissolves and continue to simmer for 10 minutes to infuse the ginger. Remove from heat, remove ginger and allow to cool. Add gelatin and allow to bloom for 5 minutes then return pan to the stove and heat until gelatin has dissolved, about 5 minutes. Spray skull molds with cooking spray and pour gelatin mixture into the mold. Allow them to cool and firm up on the counter. Unmold and refrigerate until ready to use.