Why not just use CSS add to offset one of the icons?
<span class="fa-stack fa-lg"> <i class="fa fa-file fa-stack-2x"></i> <i class="fa fa-file fa-stack-2x" style="padding-left:15px;padding-top:15px;"></i> </span>
Fiddle: http://jsfiddle.net/mwatz122/sx7fk582/
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