I ran into a snag getting share buttons from a bunch of different plugins to work on the custom homepage. They worked on single posts, regular posts, pages, everything, but would not show on the custom homepage. Quick fix (I'm all ears if there is a cleaner way!!!) is to just add the stock FB code for the share button into home.php.
right after the line containing the locate_template function positioned the button centered right below the box of custom homepage text .. voila... happy client...