Not possible, actually.
The Cable line carries an FM signal, which requires a cable modem to decode it to an Ethernet signal. IF the neighbor has a cable modem of their own, then they could possibly be using the same physical cable to attach to the Cablevision network, but I would assume that Rogers would have had to activate that, and it would not be on your account.
IIRC the number of neighbors that you have attached in your local area does affect your maximum speed, but that is inevitable whether or not they are in the same building.
Cable Speed - How Fast Is Cable Modem Internet?