You could probably add a way to override the velocities or add to the existing calculations (which will require some code changes most likely), but the problem is that will blur everything on the material, not just the silhouette or alpha. I’m not sure exactly where you’d need to look, it may require a new “CustomOutput” style node to be created in code and placed in order to define the custom motion vectors. You’d need to find where the motion vectors are rendered. One starting breadcrumb I know of is to search for the “Accurate velocities from Vertex Deformation” project setting which will lead to a define which will lead to a variable you can search for to see where the motion vectors are calculated. That project setting allows the “worldposition offset” input to be input as motion vectors into the base pass, so if you find that location you can find where to override.