Certainly you have a unique challenge,but one I think you can manage with time and money. I would consider these options:
-can the current living space be modified in any manner to accommodate a bath?
-can you make the units look high end and carry that into the baths to look more like a bathroom in ana expensive club?
-find the fixtures,tile and double or multiple shower heads
-provide every new resident a nice white cotton robe and some shower shoes (flip flops) have the robes emblazzed with your apartments name
-change the look of the landscape and provide a high end appeal
-partner with local business to provide discounts for your residents to enhance value
-perception of value crowned by pride of residency
Bottom line, if you can't buy your way out of the problem, your going to have to price your way out.