Render to specific cubemap mip

  Hey all! 

I am starting to implement dynamic cubemaps in my renderer. I have to top level mip by rendering 6 faces into 6 separate RTs. I then merge them into a cubemap. 

All of this is fine, I now want to filter the mips with some brdf convolution a-la UE4.  I can't find how can I render to a specific mip of the cubemap? I assume I need to render to different cubemaps and then merge them into a mip chain? How can I do this? I am not finding info online...  

To be clear, I am not asking for the convolution technique per se, but just how to set the render to separate mips in d3d or how to merge separate targets into a mip chain. 

Thank you very much

Jacques