Most excellent question! Very clear, included a link and everything.
So here's the deal:
By default there are two attributes that are automatically assigned values if you do not overwrite them:
'float' => 'left',
'display' => 'inline'
so, what you will want to do is the following:
1. in your shortcode, always assign the float attributes with a blank value, like-a so:
[column class="post_column_1" float=""]bla bla bla[/column]
[column class="post_column_2" float=""]bla bla bla[/column]
2. In your responsive css, you would define
.post_column_1, .post_column_2 to float: left or float: none as needed.
Get it? Good! Please let us know of your trumpeting success with this... so we may uncross our fingers, unpress our thumbs.
To the Disco!