Here's a excerpt from win7 forum:
This is the only work around I have found.
1. Create a folder on your hard drive for shares. i.e. c:\share
2. Create another folder in the above share. i.e. c:\share\music
2. Link the Library to this folder.
3. Delete the folder.
4. Use the mklink in an elevated command prompt to make a symbolic link. Name the link the same as the folder you created above.
i.e - mklink /d c:\share\music \\server\music
5. Done. Now you have non-indexed UNC path as a library.
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The reason I asked about linux file share is because this will not work with a linux file share.