We often use a softening agent using glycerine for softening gnarly veneers, like burl and crotch. I wonder if it might help in turning, too. I can imagine one reason it might not be effective, because the veneer is so thin that the glycerine can soak all the way through in a hurry, but the bowl blank might need to soak for quite a while. There are several different recipes on the web for this agent, using such additives as alcohol, water, glue, etc. I would not try one that includes glue, as that would make it harder. If you want to try it, experiment first on something that is not valuable.