double volumetric phase

[nKo]

Hi,
Is there any way to combine 2 volumetric shaders to use both reflective and transmitive phase ?
Or simply have a shader with 2 phases and a blend factor.
I do this trick in our render engine at work to have better volumetric cloud rendering, and it's really imortant for rendering high transmitives medium as snow, sugar or clouds.

Any idea ??

nKo