So here's what I'm thinking... if you can find someone with cameo silver pied birds and get a hen chick -- either a white hen, so you have two W genes, or even a cameo SP hen chick, you will pick up the WE variant gene (if that's what it is), which should increase the white in the offspring. And it makes more sense to me to bring in one more hen rather than, as you say, expand the pens for another male. And whatever you get from the present hen you have is what you get... but I tend to thing of these things as very long-term projects
If @AugeredIn tried to wade through all that stuff I wrote, it probably induced a coma, and will require emergency coffee