First i am not sure if this is a limitation of Minecraft, so it it is, let me know this if it is.
I tried to set set the Amount of an floating Item over the API, so that you see the stacked item texture. But i realized, that nothing happens. So i asked my self if this is a limitation of MC, or a limitation of HolographicDisplays. And if it is a limitation of HolographicDisplays can you change this?

Added here 8293f8b