I cannot share any "complete" case studies as those are/were proprietary information, but I can tell you that I was a Master Black Belt for 12 years for a company that only used JMP for Six Sigma projects.
Even though you may not have the case studies, those customers certainly have to have them to continue to use JMP in that area.
Keep in mind that opponents to using JMP will always be able to say "yeah, but our business/industry/application is different!". Perhaps an additional approach would help? Focus on the tools and techniques required to solve your problems. Does JMP offer those tools and techniques? (the answer will be yes!). If so, then why not use JMP? It provides many advantages in the quality improvement area.