Put watermelon and blueberries in blender in small amounts along with some of the corn syrup.
Freeze in the freezer, stirring every 1/2 hour-1 hour, as I don't have a machine.
Notes
Substitutions
Corn Substitutions: Corn is a common ingredient in products. Starch, modified food starch, dextrin and maltodextrin can be from corn. Consult with your physician to find out which corn derivatives you need to avoid. Many corn-free options are available in the US. Find out more about corn substitutions.