Yeah, that'll be a tough sell in Manhattan. That place is one of the toughest places to run in the entire UCAS because the corps lock down pretty much everything. A standard pet license just won't cut it for taking the dog around the sprawl, and the license for a service animal would be a very tough sell.
My advice? Skip the service animal idea altogether. Instead, make sure he learns Spanish and Nahuatl (spelling?), wear some Aztlan-ish clothes, and claim to be part of the Path of the Sun. I know they discuss it some in the old Aztlan book, maybe in some of the others, but having an 'animal twin' is a status symbol down there. Add a fake Aztechnology SIN, and you're halfway there.