Been pondering a suspected similar problem with another bass.
Wondered if the truss rod end is a solid barrel. If so, would it be possible to drill a hole in the back of the neck, through the face that sits in the neck pocket ?
If so, once the hole is bored, would it be possible to thread a hole drilled in the truss rod barrel and screwe a bolt into the rod ?
If that is possible, the protruding bolt would prevent the rod from turning.
If it's possible, of course. It's just an idea, I've never tried it or heard of anyone doing it, so don't know if it's even feasable. If you're going to throw a neck away though, what do you have to lose ? Is it possible to discover more about the end of the truss rod to see if may work ?
I dare say a friendly Luthier will know if something like this will work.
Good luck with this one, whatever happens
T