Saving grain for later use

[Audionut]

Is there any way (perhaps with masks and such) to create a copy of the grain and perhaps fine details of video, and save that information in to a small file, with the ability to add that information back to the video at playback?

It's only an idea, I would not be able to attempt it myself, nor have I really any idea how to do it.

But I know you guy's use masks and such for denoising/sharpening/etc. Perhaps is there was a way to save that information into say a smaller than 1mb file, then use ffdshow's avisynth to insert it back in at playback.

Would be great for x264!!