implementing HDR + 8xMSAA workaround with RGBM - problem with graphics.blit to back to hdr

hey, since MSAA is my anti aliasing of choice for Virtual Reality i'm trying to work out some old game engine style fake-HDR to have great image effects later on.
Encoding standard shaders to RGBM works nicely, i can also decode them back to a RGB image with a higher range via an image effect. Problem is since i use MSAA i can't use HDR on my camera. Therefore the Renderbuffer is not RGB Float/ RGB Half. So after bliting my renderbuffer to decode it back from RGBM to HDR RGB i can't use this HDR Texture in further image effects. Like when i use a image effect after the decode_from_rgbm the values are clamped between 0-1 and the high color range is gone, so no more beautiful bloom or eye adaption possible. I guess this has something to do with the OnRenderImage source beeing in a LDR Format.
Anyone has an idea for a workaround or how to change my LDR Rendertexture after my first graphics.blit to a RGB Float texture to keep the high dynamic range?
My Idea was maybe i can overwrite the following source-rendertextures with my own or something...

 

You might get some ideas from this:
https://forum.unity3d.com/threads/bloom-only-emissive-surfaces-in-forward-renderer.408645/

That's trying to deal with it in a different way, and it currently has some bugs for VR, like point lights only rendering in one eye. You might be able to change the camera's rendertarget at some point after rendering but before image effects.

Unity 5.6 should support this natively.

 

uhm... nice, so HDR with MSAA basically is possible? that's a much better approach. Will try asap thank you very much