It does seem like he did a sort of self-replication. And yes, he can manage to make it because he's CLOW and he kicks ass. If Syaoran managed to give an empty copy half his heart when he was SEVEN, Clow managing to create his own reincarnations seems perfectly plausible XD

And I'm sure FWR was all butthurt over the fact that Clow could make perfect 'replicas' (in a way, since it's not exactly a replica but a reincarnation e_e) and he had all those failed copies.