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you could probably fly a 777 in formation with another one, but not at the required distance as to become one single target. That distance is dependent of the resolution of the radar used. However the early 1960 Radars were capable of resolutions of less than 600 ft, modern are down to 300 ft of resolution. As shadow formation you would have to fit within the resolution of the radar.
Nope, not with an airliner...