Overlayfs for 3.10

I don't know about overlayfs, but considering /etc/ is tiny you could achieve the same result by copying the global components to a local ramdisk/tmpfs and mount-bind the client-specific NFS files/directories one by one with a script. If you don't need local rw, just bind directly on top of the global fs. Or do it the other way round, bind the global fs components on top of the NFS, whatever is more convenient.