Shower Use by Non-FTEs

Shower calcs only look at FTEs and not transients or visitors. I have an office building TI that is putting in a fitness center with a locker room scenario. The locker room will have no urinals and both regular and ADA showers which have different flow rates. Meaning I will need separate fixture groups that I can assign different users to. This LEED project has a small footprint and very small FTE count that is commensurate with the size of the space and the few new FTEs associated with it. However, the building is full of people that will be using the showers. How would I reflect the actual use of the showers that is a building wide issue vs. the LEED area boundary of the small TI with its small FTE headcount? Do I plug in the whole building FTE count as transients than force a daily use of 0.1? With respect to the lack of urinals, the locker room also sits across the hall from core bathrooms that have urinals. And of course there are other urinals in the building. How do I establish how many of these locker room users who are showering would actually also use the toilet? As opposed to the other restrooms in the building that do have them? Any suggestions? Or experiences along these lines?