Short version...
First you make an image series of random gray scale blobs. It should have as many images as a multi-pass setting. (9, 16, 25, etc...)
Apply that to your model. Set it as a displacement map.
In the chor, Set the frame property of the image sequence to cycle through the series in the first 0.2 of the first frame and set that to repeat for every frame
Render with multipass, 20% motion blur
All the different displacement maps blurred together make a fuzzy look.
sample PRJ...
scratchWhiteTest.zip