try dragging a crafting table over to him, tipping it over and propping something under it so it *just* clips the crafting hitbox into kerfus, and turning him into parts; You can craft them back into a functional kerfus again after gathering the bits. I don't know if it will actually work but I have freed kerfus stuck in weird situations like that before, though I will warn that you may lose kerfus parts below the ground still.... actual spoilers below though if you do lose parts v v v v v v
you will need two kerfuses... kerfi? for a crafting blueprint you can find, but there is extra parts after, so it's not a total waste if you lose some parts