I'm not sure what a laxative will do for the oviduct. Doesn't make sense to me. Is he an avian vet or just a regular vet?
I once had a hen with a huge egg we could feel, hard as a rock. The problem was that it was no longer in the oviduct, but had dropped into the abdomen because it had another egg inside it and was too large to pass through at all. An egg in the abdomen is a death sentence without surgery, but hens usually don't survive surgery anyway, seems to me.
The best defense against internal laying is probably get away from bad stock entirely. Good quality breeder stock, and I do mean breeder, not just propagator of hatchery stock, seems to have better genetics, overall. They are not immune, of course, but you'll see much less of it with better genetics. My good quality Orpingtons and Ameraucanas have not had any reproductive issues whatsoever. Some are over 5 years old and still laying.