How do you disable Cron on a staging / dev server? I have a staging and dev setup, but I wonder if I can disable cron on these as I don't want cron firing. It's mainly because I have backup migrate module scheduled to backup my site everyday, but I don't want this executing every time.
Yes, you can do this in your settings.php file (as you have mentioned that is the only difference between versions).

You would do it like this (in your settings.php file):

// Disable drupal's built in cron trigger.
$conf['cron_safe_threshold'] = 0;


For more information see Defining variables in a site's settings.php $conf array.

Edit
How this works is:


Variables are loaded from the database (or the cache if they have already been cached).
If those variables were not already in the cache they are saved to the cache.
The $conf variables from the settings file are added to the variables and take precedence over variables from the database.


So variables from the database are cached, but variables from settings.php are not.