Contactless non-ferrous metals hardening?
From this link I could find a few non-ferrous systems which show quench-induced or stress-induced martensite . Generally non-ferrous systems dont show this behaviour and they are hardened/strengthened by Precipitation hardening, work hardening, Solid Solution Strengthening.

Also work hardening is basically working/deforming the material plastically to strengthen it. So you can't work harden a material without contact. Induction hardening is used mainly for Case Hardening which is different from hardening(done to bulk of the material). So as long as the non-ferrous alloy is conductive and resistive , Induction hardening is enough for case-hardening.

And if it is hardening , the above mentioned methods are used for non-ferrous. Only the quenching/martensitic transformation is limited to limited systems.