I understand you don't want to make the commands editable on the
preferences dialog. It would be very nice though, to be able to edit most
of them (not only eject) at least in gconf. The volume commands are not so
important, but for the rest I'd like to be able to reconfigure them.

Alternatively you can provide a way to have an external configuration file
which can provide additional commands to those built in. E.g.:

<application label="Evolution">
  <command label="start" action="evolution"/>
  <command label="new mail" action="[don't remember]/>
</application>

<application label="Silpheed>
  <command label="start" action="silpheed"/>
</application>

So some applications or power users can register additional commands to
choose from in the preferences dialog.