How to use Drush with Apache Directives?
This is not a Drush function; it is a BASH function.  For example, you could do this:

DB_NAME=mydbestting drush status

Optionally, you could set your DB_NAME environment variable in your .bashrc file.

However, this is probably not what you want.  You would probably prefer to have Drush set the environment variable for you, after you specify the alias.  Drush does not have this feature, but there has been some discussion of it in the issue queue on drupal.org:

https://drupal.org/node/1848766