Combining z-transparency and mask-transparency in BI


i’m not sure if this is the right subforum for my question so if i missed the right forum please accept my apologies.

My problem is:

I like to combine a cycles rendered scene with some bi rendered volumetric fog. That should be pretty easy when i copy my cycles scene to a new bi scene and change all materials and use the bi mask transparency.
But i have some trees in my scene which are using a alpha texture for their leaves. Now, when i change the material transparency to mask the whole leave mesh and not only the texture leaves are masked.

is there any possibility to combine both z and mask transparency. (Z for the invisible part of the leaves mesh and mask for the textured parts of the mesh)

Simplyfied setup of the scene

Mask Transparency (everything behind leave texture is masked)

Z-Transparency (not needed parts of the mesh are complete transparent)

Thanks in advance for your help

I would just add a copy of the leaf texture to use as a color map (alpha should be unaffected so long as the color map is used before the alpha map).