Help with the drushrc.php file

I have Drush and Drush_mm up and running on a new multisite installation of Drupal 6.9. The directory structure is like so:

/drupal-6/sites/all/modules/contrib/ (drush, drush_mm, and the many more modules I will be installing with Drush!)
/drupal-6/sites/all/modules/custom/ (all site custom themes)
/drupal-6/sites/all/themes/contrib/ (all site themes)
/drupal-6/sites/all/themes/custom/ (all site custom themes)

/drupal-6/sites/siteOne/modules/contrib/ (siteOne specific modules)
/drupal-6/sites/siteOne/modules/custom/ (siteOne specific custom modules)
/drupal-6/sites/siteOne/modules/themes/ (siteOne specific themes)
/drupal-6/sites/siteOne/modules/themes/ (siteOne specific themes)

/drupal-6/sites/siteTwo/modules/contrib/ (siteTwo specific modules)
/drupal-6/sites/siteTwo/modules/custom/ (siteTwo specific custom modules)
/drupal-6/sites/siteTwo/modules/themes/ (siteTwo specific themes)
/drupal-6/sites/siteTwo/modules/themes/ (siteTwo specific themes)

/drupal-6/sites/siteThree/modules/contrib/ (siteThree specific modules)
/drupal-6/sites/siteThree/modules/custom/ (siteThree specific custom modules)
/drupal-6/sites/siteThree/modules/themes/ (siteThree specific themes)
/drupal-6/sites/siteThree/modules/themes/ (siteThree specific themes)

etc.

My understanding is, if I want to install a module or ten, I best navigate to:
/drupal-6/sites/all/modules/
and then run drush -l http://www.siteOne.com pm install image img_assist captcha etc?

But if I wanted to install a module that was specific to a certain site, I would navigate to
/drupal-6/sites/siteTwo/modules/contrib/
and then run drush -l http://www.siteTwo.com pm install ubercart etc

Now, my question is, can the drushrc.php file help me out with any of this? I see a switch for the "-l" option, but is there a way to set multiple lines with a "-l" option for the various url's that exist on a multisite install?

Also, for updates, is it necessary to navigate to each site to run drush -l http://siteOne.com pm update, or is there a way to run the command once and have Drush update all modules across sites?

Oh, and one more item... does Drush install and update themes as well?

Thanks