Best way to restrict Domain Mapping option to Network Admins

Hi, what is the best way to restrict the Domain Mapping option to Network Admins only? We do Domain Mapping on a case by case basis and like to handle it for the site owners. Most of the DNS changes are done on our own network, so we have to do some work before mapping the domain. We used to edit the domain-mapping.php file on an older version (from advice given on this forum) to only allow super_admin access. Version 3.1.6 is very different, so I'm not sure if this is still an option or not.

Thank you.