It was tested by NASA and the US Air Force.
Using the station keeping mode in the fms, they were able to offset fly on autopilot. (Station keeping is how bombers fly in configuration, and dont hit each other with the ordinance being dropped)
It worked very well for fuel consumption purposes, but the aircraft offsets to effectivly 'ride' the uplift part of the vortex are on the order of 10 aircraft lengths by one wingspan offset each side of the leading aircraft centerline.
It was quite amazing, with the lead aircraft on a coded centerline, the trailing aircraft would offset 10 by one in the FMS from the associated leader, hence forming a perfect 'V' formation. In addition to the trailing length, the systems has the capability to offset by ticks, the H and V from the leader.
They did this with 9 C-17 aircraft from Edwards AFB to Charleston, SC, alternating the offset configuration along the flight, to optimize the configuration.
While the concept worked, there is no way you would have commercial aircraft in that tight of an offset enroute.
Formation flight system keeps C-17s in line
