Modeling HVAC for future un-designed office space

I am modeling a 50,000 sf college cafeteria that has a basement, a main floor and a mezzanine. A portion of the basement is part of the cafeteria. About 11,000 sf of the basement has been reserved as a future office space that will not be designed or fitted out until a later date and is not part of the design team's scope except as a core and shell space. It will have its own entrance and the using entity will be a department of the college. The cafeteria building will be served by district fossil fuel steam heat, and a cooling tower with condenser loop will serve a number of water-source heat pumps for cooling and heating. The capacities of the heating and cooling loops have been sized to accommodate the future office space loads. The office space does have a separate mechanical/electrical room. The delivery portion of the HVAC system has not been designed, but I think it is unlikely to be designed with a system that does not tie into the systems that will serve the cafeteria. My question arises from reviewing ASHRAE 90.1-2007 Appendix G, Table G3.1 Section 10, as well a few of the posts on this forum. Since the future office space HVAC is not fully designed as part of the project scope, but is within the boundaries of the LEED project, I believe I need to model it as a fully occupied space (according to what I'm reading in forum posts).  Since the HVAC system is not fully designed, it doesn't seem to fit exactly within Section 10b. But since the capacities of the cafeteria HVAC system will, by design, accommodate the future office space, the situation doesn't seem to fit Sections 10c and 10d where no heating system or no cooling system has been specified. Can I autosize water-source heat pumps, similar to others in the building, tied into the heating and cooling loops, and use this as a Proposed Design for the office space? In turn the exact same system(s) would be used In the Baseline model.