Here's what you do.

Take a male pastel or super pastel and breed it to a female piebald.

If you produce a male pastel het piebald, raise him up and breed him back to the female piebald. You'll have a 1/4 chance of producing a Pastel Piebald.

That's the quick way to cross a co-dominant mutation with a simple recessive mutation.

Using the same breeding colony to create a Super Pastel Piebald, breed the Pastel Piebald, regardless of sex, to a pastel het piebald produced from the first clutch and you'll have a 1/8 chance of producing a Super Pastel Piebald.