The fact is that the Steinberger neck is designed for stiffness and does not allow variations of relief for different styles of playing. On my upgrade necks this poses no problem, because you can easily adjust the relief without removing the neck. There is another high quality neck available on the market that I also carry, At this time it does not provide for adjustment without removing the neck entirely. If you own already one of these I can modify it for you in about 1 hour's time. Steinberger uses a Phenolic fingerboard exclusively on all of their necks.
Phenol is the prime ingredient in Epoxy.
But understand that Phenolithylin has no memory like real wood. I know you thought your Steinberger neck was totally indestructible. It would be totally unrepairable even if you did have a truss rod it could not be fixed. I keep several of each model in stock at all times. I can also satinize either your existing stock neck or a new stock neck for a small fee, if you feel inclined to do so.