I know some airlines use CASS verification for international travel in the back. About 3 years ago, I got a jump-seat from SEA to NRT on United with no difficulties, then returning to the states from KIX, the UAL Captain wanted CASS verification retuning to the US. We did not have CASS at the time, so I did some alternative arrangements.
However, I do not think that airlines are allowing jump-seaters in the cockpit for international jump-seats based on CASS. As I mentioned earlier, there is another program for that which requires minimum 24 hours notice and independent verification, where CASS is a walkup ystem. OTOH, I think it is silly to have the other program when most airlines use valid passports along with the company ID for CASS Verification anyway, and if you are CASS eligible, your picture is in the system.
So - who are you working for, onewith wings?