Module builder as drush plugin
Thanks to Clive comments, and as explained in Drupal, Drush aliases and how to use them, I solved it as following. 

Add an alias conf file named sitename.aliases.drushrc.php in .drush folder in your home directory :

/**
 * Local
 */
// The site in sites/default/
$aliases['default.local'] = array(
  'uri' =&gt; 'default',
  'root' =&gt; '/path/to/drupal',
  'path-aliases' =&gt; array(
    '%dump-dir' =&gt; '/tmp'
  ),
);
// The site in sites/sitename/ 
$aliases['sitename.local'] = array(
  'uri' =&gt; 'sitename_URI',
  'root' =&gt; '/path/to/drupal',
  'path-aliases' =&gt; array(
    '%dump-dir' =&gt; '/tmp'
  ),
);


Don't forget to clear cache : drush cache-clear drush.

Test your alias : @sitename.local status.

Now you can run i.e @sitename.local mb mymodule hook1 hook2 --write 

Really powerful !

See Drush multi-site aliases for complete configuration of local/remote aliases