My workmate claims that Milbank or some manufacturer makes a multi-position adapter for a single meter socket. Two meters plug into a Y, then into the single meter opening, put the lock ring back on. I have never heard of/seen one. 
I have seen cans though.
Milbank multi-position meter sockets.
www.milbankworks.com

I have seen cans though.
Milbank multi-position meter sockets.

Milbank - Multi-Position Meter Sockets
Milbank's multi-position meter sockets meet the needs of apartments, condominiums, and other applications where two or more meters are required.