How to get texture influence on the global bottom of an object

Hi everyone,

Hope you can help me out. I’m using blender internal and want to have particles emitting from the bottom of the object regardless of the objects rotation. In fig_1 and fig_2 I am able to get this to work for x and y but not z. In fig_3 I’m showing how you can accomplish this with a texture but the highlighted settings are not available for a particle texture.

Thanks in advance.