Is such a thing even possible?
This. In Chapter 1002, Zoro nearly replicated Ryuma's Dragon Slaying feat on the Rooftop using a posture and stance that directly mirrored Ryuma's own:
The technique โ Hiryuu Kaen โ was the same technique that Zoro used to defeat Ryuma:
The attack missed, but perhaps it was simply too early. In order to replicate Ryuma's legend, Zoro would need to perform the feat in front of several witnesses (perhaps he gets another chance when they reach the Flower Capital).