I've never done the beer can chix on the WSM, but after a few times of doing them on the grill, I gave them up...seemed too much like rotisserie chicken to me...almost identical.  I love the idea of smoking them because I think the meat would be flavored better, but not sure about the skin texture, and the temps do seem to be too low to get the good steaming.  Still, I haven't done it.  Better cooks probably can do it just fine..