After looking at the image again, I found I wasn't happy with the way the transposed faces turned out. The dot pattern just didn't seem to match the style of the base comic.
Thank goodness for software! I copied each of the faces to a separate drawing and converted it to a 1-bit black and white image which creates a reasonable dot pattern. This was then copied back into the original drawing and placed on top of the original faces. Changing the transparency of the black and white image allowed the underlying color to come through.
It's not a perfect solution (I wish there was a reasonably priced add-in that would crate the comic page effect), but it gets a lot closer to looking correct.
Anybody have a better way?