Pass positional arguments to drush via drushrc.php?
Alas, there is no command-specific argument feature in Drush.  You can't even use a pre-command hook to fill in the arguments, as Drush will check for required arguments before calling any command hooks.

Another option would be to define a shell alias, and define your argument there:

$options['shell-aliases']['myis'] = 'site-install xyzzy';


Then you can use this as drush myis [other options], and your profile name will be inserted.