Rafael,
From your direct e-mail to me, you are using this website for more of an Intranet where the information about people can be available to all. I will answer here so more people can see it.
Dave, the developer of this extension may have a suggestion, but I can think of a few options that might work:
1. You could make registration and the staff directory separate. You can set up the staff directory so everyone who is registered can administrate the staff directory. Then they can add themselves (and others if needed) and change the records at any time. We use the staff directory this way internally within WEC to have a shared contact list that we can all refer to. I love it! We can all add an update entries. The only drawback is that anyone can modify any entry.
2. If there are not that many people and the staff do not change too often, it would probably not be that hard to manually check the staff option and to add the staff record for each person.
3. I have not done this, but you could just use the FE user data table and list the users from that. Then there is no need to use the staff directory at all. I think there are some extensions that can help with listing FE user records too. FE records have a lot of fields so that may be all you need. Of course, this would be a totally automatic solution. If you needed categories like departments then those could be FE user groups.
Sorry I do not have an easier solution. This extension was not designed for this so solutions are not as nice.
In Christ,
Mark