Is there any means of taking some of the Lich’s built in healing, namely healing from damage such as leech over to ward? I know that some abilities have a mechanism for this, but I don’t recall seeing anything for leech to ward. Is there perhaps a unique for it?
No there is nothing simialr to what you describe.
There are countless different ways to generate ward, but nothing that involves leech or any conversion of health you gain.
The closest thing to that would be Twisted Heart of Uhkeiros, which heavily rewards you for having a lot of health, while being able to constantly leech it back up.
Nice idea though