We don't have any explanation but I don't think it is even necessary. Afrer all hemalurgy works by attaching a piece of soul to another entity. If the same piece of soul is attached to two entitys (Like ghost and an empty body), it could easilly work as some sotr of bridge. Moreover Hemalurgy twists the bodies of its users to make suplement damages caused by it, liike Inquistor spikes in their brain - it could easilly be a case of planned overcorrection. It also is capable of drastically changing souls and bodies - I belive it is implied that it is possible to create Kandra with only Hemalurgy from human if you know what you are doing, and if Kandra are doable then there is REALLY much that can be done in the "right" hands.
Szmit's post in How does "The Sovereign" work? was marked as the answer