hey i found a recipe for SB kethcup...
48 ounces tomato juice
1/2 cup vinegar
2 tablespoons sugar substitute
1 teaspoon dry chopped onion
1 teaspoon dry chopped garlic
1 teaspoon dry chopped green pepper
Boil all ingredients together until thick and reduced to about half the amount of liquid. Store in refrigerator.
presumably you would blend it if you want the ketchup to be 'smooth'
If you want a Cocktail Sauce...all cocktail sauce is is ketchup and horseradish (and sugar if you like it sweeter). Once you make the ketchup above, just add horseradish.