I think it's not that easy to get AUFS working with NFS on WDTV... IIRC b-rad tried to implement the AUFS patch for NFS and it doesn't work on WDTV due to some missing symbols in kernel (which we can't change).
I think b-rad even tried some tricks to add those symbols with even more nasty hacks and preloads but it didn't work AFAIK.
PS: Just found this post of yours KAD
have you tried this yet? Do you need an aufs with the mentioned compile option? I could try to recompile aufs with this option....