Tammy, I'm not quite understanding your statement about using BiPAP for at least an hour each day. Many PALS start off using it only when sleeping, when it is most difficult for the body to expel enough CO2. The decision and schedule about adding it during the day is different for everyone.
Case series for RIGs under BiPAP have studied PALS with 17%-25% FVC with successful placement. The anatomy of the PALS' GI tract (like if the stomach is out of place), their nutritional status and oximetry (BiPAP working OK), are all more important to success than FVC, based on studies to date.