Here is a picture of what I imagine the membrane that provide the snap would look like, I would produce the membrane out a a different material and it would be embedded in a material similar to what apple uses to their current band lineup.
This picture shows that the current material Apple uses is filmsy and would be hard for a person with one arm to work with. The prototyped side has the membrane in it that holds its form until released. A fulcrum point would be needed to push the band off as well as trigger the band to snap on.