Don't see why they don't do this as a matter of course- has always seemed a bit of a waste of a 57 just to haul in the empty stock for a mile or so.
Or alternatively grab a few of those spare MK3 DVTs▸ form Long Marston and operate the sleeper in push-pull mode.
given the reliability of the 57's in the west and steep gradients on parts of the route probably a bad idea, however i agree it would save money if all things were even