Add sidebar to front page twentytwelve template?

I’d like to add a sidebar (in addition to the two widget positions at the bottom) to the twentytwelve front page template. I’ve tried adding:

<?php get_sidebar(); ?>

Above

<?php get_sidebar( ‘front’ ); ?>

But nothing appears (even when I put a widget in the Main Sidebar).

What else do I need to do?

Thanks,

John