I do ALL of the smartskins for a bone in one relationship.
See this series of videos for boring details: http://www.youtube.com/watch?v=H0kRXN1XU7g...BF44797CD8BC2A3
On my current model, I have even dispensed with fan bones! I weight the joint, then in my test action I roll the bone 90º or so and fix the squeeze in the smartskin relationship. I move through all of the extreme positions in that action, right-clicking and going back into the smartskin1 relationship to reshape the mesh