I would expect that any staffed station would have arrangements for boarding disabled passengers. At my home station, Richmond, VA, the Station Agent, who doubles as the Red Cap, takes those needing special assistance out to the train in a golf cart well before the general boarding announcement.
It would be best to arrive a bit earlier than the 30 minute suggested minimum and speak directly with the appropriate person. If you are willing to share the station where you will be boarding there may be some members and guests who know the process there and can share some details. There are some pretty smart and savvy travelers that hang around here.