I'm currently working on this project (and so many more) and here is how I'm doing it:
I purchased a yearling black pastel female het pied.
I am going to breed her when she is ready to my piebald male in hopes for a black pastel pied male.
In six months, when that male is ready, he is breeding back to her for a panda pied. (the odds of getting a panda pied in this pairing is 1 in 8, which is a lot better than 1 in 16)
Voila!!