Convey Shader texture to Light Cookie

Hey guys just find out a interesting question where i couldn't find answer anywhere.

i was trying to pull a realtime shader graphic like perlin-noise realtime animation and use it as light cookie and cookie for volumetric light render (which you can find here). so i could have a dynamic light cookie constantly shapeshifting itself, like this one in real life .

 

Anyone has any idea how to do that in unity?
Only find this one in form which is playback a sequence of images.

 

Light cookies only use the alpha channel of the texture assigned. You should be able to assign a render texture to the light, and then have your shader write exclusively to the alpha color.

A custom render texture should work here.
https://docs.unity3d.com/Manual/CustomRenderTextures.html