Let's rewind for a second, and ask where and when those NFS homedirs are mounted. I suppose this is not done on-the-fly when users log in, that this is so for a reason, and that the whole infrastructure is already designed such that new user homedirs are created with at least the basics in place for them to work.
That could include making the default XDG_CACHE_HOME location a symlink to a path that will resolve locally on every system from which users can log in. My other suggested solution, a "bind mount" could be done dynamically, and since this needs to be done with privileges it might be easier to do from a login manager, without running into race conditions. I just don't know if doing a "mount bind" on host A will still allow the same action to take place on host B or C (supposing users can log in from multiple workstations).
