Whats the best method to create an email which has two columns (main and sidebar) on desktop, but has a single column which alternates main and sidebar content on mobile?

I've managed to achieve this using Foundation for Emails but since the main and sidebar content is of unequal heights, the sidebar has unsightly gaps where the "rows" fall.

Here's the desired effect:

Responsive email layout

I've also considered duplicating the sidebar content in the main column and then hiding/showing on mobile/desktop - I believe this may not be a good solution as (from Foundation's own docs) its not reliably possible to hide elements on all email clients - help!