Vista Tutorial - XDocument Exclusive Access

I can successfully do the following:

xdocument doc = xdocument.load(... my file);
xelement bla = doc.descendants.("it").first();
.... do stuff ...
doc.save("myfile");

the above works great. however, i want to interact with the file with
exclusive access so that no other files can open it/write to it/etc. while
i'm doing stuff with it.

i know that there's the normal FileStream.open (etc., fileshare.none), but
the xdocument class doesn't take a stream as a constructor.

is there any way i can do this without having to use the xmldocument class?

Thanks.