Sorry for the delay in responding. After some playing around, I came up with this solution. If you add the columns using the Template Builder then there's automatic class name added to each column called flex_column_#. The # of course is replaced with 1, 2, and 3 accordingly.
In case you haven't used the Template Builder yet, here's the instructions:
1) Go to Choices > Template Builder
2) Select the "Frontpage" template
3) Under "Add Elements" select Columns then click the down arrow on the grey tab
4) Set your options accordingly (in your case I would use Direct Text input then enter your shortcode info)
5) Click Save All Changes
Let me know if this doesn't work or you need help. I'm going to tag myself to this thread so I don't lose it again.