Splitting UDIMs into seperate texture sets in Painter?

CheeseOnToast

Here's the context. I've been working on some base skin textures intended for use throughout the project. The model will eventually be split into two materials, head and body. For covenience I've set them up as UDIMs for now so I don't have to do everything twice, and it makes working around the seam area a breeze. I'm at the point now where I'm ready to commit to splitting them into two discrete texture sets. I'd like to keep the layer stack intact when I do this. I could swear I've seen an option to do that somewhere before, but I can't find it now for the life of me. Any suggestions?