Custom Depth on Additive Material?

My goal is to always render my additive material (a volumetric fog material) behind any objects in the scene, except the sky sphere. Since the material must be Additive, I cannot use the Pixel Depth Offset pin in the material, nor the Scene Depth node. I can’t use Translucency Sort Priority either for the same reason.

For context, I’m this material is for a Northern Lights particle system. In order to get the perspective right, the system must be close to the character. Unfortunately this also allows the system to occlude other surfaces in the scene, revealing that the Northern Lights are not super-massive, but instead just close to the camera.

Any suggestions are welcome, even if they are not full solutions. Thanks in advance.

Did you find a solution or alternative?

Unfortunately no. I just moved on to something else. I’ve been thinking of using trueSky source code and adding a northern lights effect through their system, as that would probably make my job easier. But other than that, no I have no solutions yet.

Right now I’m having that problem, did you get anything?