in uscript you could write a custom player pawn, which could easily pass the location onto the material as a vector 3, since there is a method to get player location in uscript and uscript isnt limited to olny dealing with constants like kismet.
Like I said, this is hacky, and easy for artists who have no intention of coding to set up. I'll be looking into uScript options a bit later down the road and post what I come up with for sure!