Twenty Twelve use id="secondary" for both sidebar and sidebar-front, this means if we add the call to sidebar on front-page.php there will be duplicate id on one page.
You can, however, make another copy of sidebar.php and rename it to something else like sidebar-main.php and inside it change id="secondary" to id="sidebar-main". Then in your child theme, make a copy of front-page.php with a call to this sidebar we’ve just made above the get_sidebar('front'). Also, there will be quit a bit of CSS adjustments to do.
You need to make a child theme first, the site you link to uses 2012 straight, it should be a child theme using 2012 as a parent theme. Any modification will be done in child theme only, leaving parent theme as is.