Rendering unpremultiplied Alpha

[nomads]

so you still have to render twice.

[Khazmadu]

so you still have to render twice.

No you don't. But the rendertime will be a bit higher since there is another Channel that must be calculated.
The Vray Placement node is mapping the Texture like an Enviroment map. So it doesn't matter what geometry is there every object will get this texture.
Just try it you will see it works

[nomads]

Hi,

I got it working by putting a VrayMtlWrapper on my environment sphere. And my environment material in the extra texture.

Thanks for the tips