external image as velocity layer for vector blur


I was wondering if it is possible to use an externally rendered velocity layer with the vector blur node? I have an image with XYZ to RGB mapping of velocity. I can imagine that blender uses something similar in the speed layer that you normally use as an input. If this is not possible, is there another way of tackling this problem (aside from doing my whole project in blender, something i want to try sometime in the near futere :slight_smile: )