H
Heisenberg
The answer lies with ignorance
Run 2 cables,take one into a socket and let the other ignore that socket
Run the cables to the next and one of the cables ignores that socket
(the cable that ignores the socket matters not)
When you get to the end of the run,terminate them both at that socket
But surely if you are not sure which cable (leg) is ignoring that socket, you could be putting all the sockets on the same leg? i.e. one of the cables that is terminated at the final socket could have no sockets on it and simply go straight back to the CU.