Yes, this is possible, but each additional driver must register to the CarAmigo platform (and passed all profile criteria). He/ she also needs to be explicitly mentioned on the carsharing contract. 

In order to add an additional driver to a reservation, click the field "add an additional driver".

Insert the e-mail address the new driver used to register to the CarAmigo website. If the additional driver does not yet have a registration on CarAmigo, he/she will receive an invitation to signup at that email address.