Pre-Rendered Background Shadow Question

Hey! Can anyone point me in the right direction for getting dynamic shadows to be displayed onto a fully transparent mesh? I’ve spent a couple days and understand the limitations of translucent blend mode and how shadows work, but just looking for maybe some type of work around?

I have a post process displaying a Pre-Rendered image and want the characters shadow to be displayed over this dynamically. Need’s to be a high quality representation of the character, not just a circular shadow.

Good amount of half-solutions on the forums here but none seemed to have worked for me, or aren’t really performant for a full game.

Thanks!