Yes. The 2nd passenger's ticket is called an "open sleeper ticket" and it requires an agent to issue it. The fare difference is the rail fare, which is currently the second lowest coach bucket, not counting Saver fares. Almost always, the passenger must pick up the open sleeper ticket from a agent at a staffed station. The open sleeper ticket is an actual paper ticket (unless things have changed) and not an e-ticket.

Call the Amtrak reservation line (800.872.7245 or the number provided to you by AGR) and speak to an agent. If the agent seems at all confused or hesitant, ask for a supervisor. "Open sleeper ticket" is the buzz phrase and many agents do not know about them or do not know how to issue one.

Usually I have heard about open sleeper tickets in the context of a second passenger who is joining the train after the first passenger or departing before the first passenger (or both). I do not believe one can be issued for a second passenger who will join the train earlier or depart the train later than the first passenger.

Good luck.