@seafansar
I noticed you are in Florida. I was hoping that it is perhaps a local species and therefore could be released, but it is not. Based on the information on this page:
http://www.nudipixel.net/species/ceratosoma_sinuatum/ (scroll down to locality) this critter is a Pacific Ocean species. It isn't from the Florida Atlantic coast, Gulf of Mexico, or Caribbean areas. So, taking it to the ocean for release is NOT recommended. I also double checked my Caribbean Sea Slug field guide book to verify and Ceratosoma sinuatum is not listed.
Posts on the sea slug forum state that they are not sure what this animal eats, other than it eats sponges, probably of the Dysideidae family of sponges (that is the family of sponges species of Ceratosoma usually feed on). Any chance you can order from your wholesaler the sponges from this family? And what if you can sell the Ceratosoma's and the sponges they eat to customers who want that unique reef critter? It would have to be made clear to the customer that they will have to continue to order the sponges from you for feeding it. From a business model perspective, it would be a good way to bring customers into the shop regularly (picking up their special order sponges, food for sponges, and then what ever else that the customer needs). Just a thought on how to keep these animals alive now that you have them, and perhaps help your business.