I was in a hotel room in London, England one time where they'd added a shower where they couldn't go through the floor...it was a major safety hazard! The step out of the shower with wet feet was way higher than is safe, IMHO, to be able to get the P-trap in place and then have enough slope to get to a drain (no idea if it was vented properly) requires the floor to be too high.
Depending on how the floor is made, and whether you could get the cooperation of your neighbor below you, and how the ceilings are arranged (drop ceiling?), you might be able to put in a 'normal' looking shower without the excessive floor height (is your ceiling high enough to handle a raised floor of the shower?), you might be able to do this more easily. A core drill could cut through the floor slab cleanly, if there was a way to connect it to the drainage system below.