John,
I would investigate the possibility of using estrogen patches (at 1mg dosage or similar). These have been used as third-line hormonal therapy for some time, and are also being studied in various trials.
Depending on side effects and his food intake risk assessment, he could consider taking Zytiga with food. This is not the standard way of intake. However, this study has shown that for some patients, taking the drug with food massively increases its potency in the body (more than 10-fold), resulting in more effective anti-PC response:
prostatecancerinfolink.net/2015/05/12/abiraterone-acetate-and-the-food-effect/ Ketoconezole has been reported to work, when Zytiga does not. So that would definitely be another avenue to pursue.
Lastly, Xtandi's manufacturer has a patient access program, which provides the drug for free. It requires an application, which is not complicated to go through. Though the implications for cross-resistance are there, it might be worth taking, if you can get it. Remember with Xtandi, it takes at least 4 weeks for the drug to reach maximum therapeutic effect (steady state in the body), so stopping it before that is premature (unless warranted by side effects).
You're so right not to accept the nurse's "prognosis". There's more to be tried, fight on!
Arthur