If necessary, remove seeds from the watermelon and blend the flesh. Pour the mixture into the ice cream mold, close it, and place it in the freezer. Once frozen, take out the ice creams and add a little orange juice to the bottom of the molds. Gently stick the ice creams back in and place them in the freezer again. If all the juice is pushed out, you can put something between the mold and the lid to hold the sticks up.