I believe that you need to have a Blu-Ray reader/writer device in order to create a Blu-Ray disc. Unfortunately, there are no advanced instructions on how to enable that option, but I've seen it in other applications as well. The Pinnacle MyDVD considers that you lack the physical device required to create Blu-ray discs, and since you don't have it, the option isn't enabled regardless if you just want to create a Bly-ray disc structure.
Additionally, if you have the software installed go to the Help > Contents to read about more about its usage.
