If you’re planning to use the texture paint solution, a brutal UV unwrap of the complete piece(with decent amount of bleeding pixel) could actually work. It’s not the most elegant solution but I’m far away from being a mesh-snob 😀
Of course, I don’t know how many faces we’re talking about. Have you tried to decimate it a little bit beforehand ? Blender’s decimate modifier performs pretty well actually.
Another solution would be to have two UV-maps for your object: one for the edge-modelled, one for the sculpted, and fine-tuning them so it looks as seamless as possible.
