Let me clarify what I asking is about desktop computers with intel iGPU and discrete nVidia card, which motherboard supports multi-GPU. I do not mean Optimus technology equipment.

Well, I had opened the following thread in nVidia dev forum:

It's about being able to use CUDA (eg Blender 3D) with discrete nVidia card, but with the intel iGPU as the primary display and the intel driver loaded.

As you can read on page 2, after doing extensive testing I asked to developers if any of them actually been able to do what I want, and I ask them to recommend the distribution in which they have managed to do it.

Do you know if it is possible?