You DO NOT list ahead of time when jumpseating on UA. It just creates more problems for the gate agent who has to delete your listing and then do it the right way. The UA system uses your CASS info to create your jumpseat listing, it is probably the fastest and easiest system of any mainline carrier.

Jumpseating back to the USA on United can be a major pain, it can be hard to find a gate agent who knows how to list a jumpseater correctly, and some stations (like BKK) just refuse to do it at all. I've gotten stuck in NRT because of this.