So, I managed to contact FWS. Here's how it works: Apply for (up to 90 days in advance!) and receive necessary permits, submitting eDecs etc as necessary. 48hrs prior to departure, phone the local FWS station and book an appointment for an FWS officer to inspect and validate your permit(s). On the day of departure, the FWS officer will meet you as arranged, usually at the check in counter area to complete the inspection and sign off the permit(s). Inspections organized after hours are subject to a (currently $200) fee.
Hopefully that's useful for somebody down the line...
