How to specify the center position of a radial blur

Hello. I am currently trying to create a radialblur post-process material for an effect, but I don’t know how to control the center position of the blur.
I guess I can just get the world position of the object I want to position and convert it to screen UVs, but I don’t know how to input the dynamic values of another object into the post-process material. Can someone please tell me how to do this?

I -think- the default position, will be the center of the PP volume. So as long as that’s around the player, you’ll be ok.