I just noticed that the particular linear pocket socket that you mention does not have association capabilities. This is an optional feature and manufacturers make a decision model by model as to whether they will include it.
There are several models that offer this. There is an older Cooper that works fine and has a number of advanced features, including association.
http://www.westsidewholesale.com/cooper-rfapm.html
Or several of the newest generation Z wave plus modules also support Association, you just need to check each one to be sure.
I think the Zooz line may, @TheSmartestHouse should know.
Again, you would only need association if you want the switches to continue to be able to control the fixture even if your smartthings cloud account is unavailable.