Using that SU command like Unix does, I think that Windows should have something like that for NT or 2000? I never investigated it, but heard about it.
Another thing you could do is have a server app program run every five minutes on the server and copy the files to an incoming directory and add an entry in the server database for the path and server name to copy to. The server program will have write access to that path even if the user does not. Sort of like a batch processing job. Every five minutes it will copy the data from the incoming directory to the real directory.