The Fostex T50RP/Shure headphones have ellipse-shaped enclosures, but the Fidelio X1 is very circular. I don't think it can be done.
Change managed to get the oval shaped 1540 pads on the HP200 which has a circular form. It's possible with enough effort as long as the pads are the correct size for the headphones to which you're trying to attach them.