When I have these kinds of file/sharing/locking issues, I usually just make a copy of the file and open that one up instead. But depending upon what you are doing that might not work for you. What have you tried so far? I know that you can specify if you are opening a file for reading only...but I'm not sure if that would solve your locking problem. Have you tried
File.OpenRead[
^]? Or have you tried
FileStream[
^] with setting the mode/access/share parms to different settings to test it?