Adding encoders to my old ABB sinusoidal servos

So I was looking at encoders over at US digital and measuring out my ABB servos trying to devise a game plan when it occurred to me that there is not as much of a stub shaft in the back as I previously thought. Attachment 249408

length from that shelf on the outer edge is maybe 2 mm despite the appearance of the shaft length from the motor internals. My only thought in order to actually pull this off is to bore out the center of that shaft to around 1/4" and thread it. Use a threaded rod to fit with red lock-tite and then lathe the new stub to the finished profile for the encoder kit to fit. I may have to machine away a small amount of the body for the connector to clear but that part of the body does not seem to be structurally critical.
Anyone have any better ideas?