Random thought: how about an alternative AEW version with a drooped nose holding a flat, 360 deg radome just below the fuselage line, a bit like the Italian EH-101 AEWs, or the BN Defender AEW? If the radome was decent depth, the S-3 might also have to have an extended and/or forwards-retracting nose gear strut for clearance, but on the flip side, that would help with take-off AoA.
Alternative, alternative AEW version: planar-array pods on the wing pylons like the AEW Sea Harrier concepts.
Radically Alternative AEW version: two or four overwing USB engines as suggested by arkon and planar array radars on the sides of the fuselage.