Modeling Mechanical Systems for Core Areas

I am working on a project that includes some limited core areas such as lobby, electrical rooms, restrooms, etc. and spaces allocated for future tenants. The HVAC systems are being designed under the core & shell project for the future tenant spaces and the core but will not be completely designed or built out. I have found that without a full design I cannot accurately model those HVAC systems and take credit for the energy efficiency associated with them. However, there is an opportunity to completely design and model the HVAC systems for the core spaces. How might I go about accurately modeling these systems in the same energy model? I am using EnergyPro V6.8.