CameraEvent before/after shadow projection

With the CommandBuffer addition to Unity 5, we get the chance to intercept specific rendering events and not be limited to PreRender/PostRender, which is awesome.

However, I don't see events for directional light shadows like AfterShadowMap (or) BeforeShadowProjection and AfterShadowProjection events listed in http://docs.unity3d.com/ScriptReference/Rendering.CameraEvent.html

I'm especially interested in the AfterShadowProjection to create volumetric particle shadows (that are cast on the scene). I'm looking at the .cginc files, but I can't edit them with Unity running, since they're read only file handles. I really want to use the existing standard material in Unity 5, but just tweak the directional light intensity based on my (projected) light propagation texture to let a particle volume cast shadows.

Attached are two screenshots of my volumetric particle system. It receives shadows from the scene (I had to reconstruct a mini-shadow map for this, since I wasn't sure how to intercept/use the shadow map) but doesn't cast any.

Hoping one of the rendering wizards sees this
Ideas to do this in the current version are very much appreciated.

Thanks.

 

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