If you have fist weapons and execute a stealth attack on some unsuspecting enemy types (iirc infested which might make things even harder), you can indeed perform the thing.
Source: I had those life-on-hit fists and was going very very fast with Volt; fast enough to unintentionally get a stealth finisher on an unsuspecting Dark Sector infested charger or something while blazing through the level punching very very fast.