I'm interested in seeing the answer as well. Of course I have a shorter growing season so it might not be feasible for me after all. I had purchased 'White Wings' because I had heard somewhere on tv that it had the potential for rebloom but it hasn't yet for me.
I don't deadhead mine, but they seem to bloom on and off. This is an older plant that I inherited with the house, and really needs to be divided. The first few years, I didn't even know what it was, but since it bloomed a pretty pink, I just left it alone.