Dunno if that really solves your problem if you are trying to avoid transferring the build over the network though. :( Maybe if you built _to_ the NAS it could run a bunch of it in parallel. (Changing the subject... get a NAS! They are reasonably cheap now and super handy.)
Unity builds are often like 90% the same. Does rsync work from Windows? You might be able to just rsync the folder over and skip all but a few megabytes to transfer.