Widgetize theme question

I am building a theme off of the twenty twelve theme and I’ve added a widgetized area to the header and it works great.

I was also able to add one to the single.php

What I would like to know is can you add one to the single.php that runs downward like a column or sidebar.

I want the information in the widgetized area to display before the comments section when viewed on a mobile device but still look like a sidebar on a computer screen.