If he needs to file the top of the steering shaft down, a pull-wire will just be in the way.
You can get even an old horn wire back down thru the bottom of the gearbox; I've done it numerous times. There are two places inside the steering shaft where the bullet connector at the end of the wire might hang up. The first will be at the top of the oil tube and the se3cond will be near the bottom there is a little indentation all around the bottom of the tube that holds it to the bearing backplate.
If you straighten the wire real good and twirl the wire while pushing it down into the shaft, it may go all the way thru for you. If it does hang up, pull the wire out, straighten it again and reinsert, pushing down and twirling the wire in the opposite direction.
I think the mistake you made which damaged the top of the shaft is by removing the nut that holds the steering wheel all the way off, leaving the top of the shaft susceptible to damage. The proper way to remove a wheel is to unscrew the shaft nut until the uppermost surface of the nut is a little higher than the top of the shaft. Then put on your steering wheel puller and insert a short piece of bar stock between the steering wheel nut and bottom of the center bolt, that way the nut and shaft endure the compression as a unit. The bar stock should be minimum 1/8"thick AND fits INSIDE the metal horn ring plate on the steering wheel.
Tighten down the SW remover center-bolt and the wheel will pop off but it wont be able to fall, because the nut is still there, which is another good thing. If the nut was gone, the wheel would pop off, fall in your lap, get scratched or chipped when it rolls off or hits the top of the column. You don't want that.
Let me guess, you have accidently expanded the steering shaft from tightening the SW remover up against the steering shaft, so the steering wheel nut wont go back on, right?
Here's what you do; get another nut with the same thread as the SW nut and clamp it in a vice. Get a Dremel tool with abraisive cutting wheel and cut a slot all the way through the short flat side of the nut. you have just created your own die for cutting the threads on your steering shaft. It may be necessary to get a small chisel-punch and drive it in the slot you made in that nut prior to attempting to screw it on the shaft. Once you get it started on the threads, pull the punch out and get a wrench and run the nut up and down on that shaft enough to re-cut the threads until your original SW nut will go on the shaft.