I am not really sure what you mean by sprinkling salt on top of it. Are you meaning a thin layer of salt between the top and the bottom? If so then I would say it would come apart.
What you could do is divide your batter in 1/2 and add salt to one of the halfs ... pour it. then let it sit a bit to thicken then pour the other over it then let it gel. Then you would have one half salt bar and the other half regular soap.
I am not sure if you would need to spray it with alcohol before pouring the top layer or not...... some do so that it will stick together but usually it is day old soaps or scraps they are putting in. Might wait for another one to comment what to do in this case.
HTH
Val