Need help adding addl driver on website for National or Avis

[juju]

We will have two drivers on our next trip, not married to each other or business associates. I received a good rate using the codes on the internet, but couldn't figure out how to add an addl driver. I am an EA member and wasn't sure how to handle all of this in advance. Guess I can call and update my internet reservation. Anyone have any experience with this. btw, I am also a member of Avis' express service too.