Free additional driver in Europe
 

I attained Sixt Platinum through a hotel elite membership and, when searching for a car in Portugal, was surprised that Sixt Plat does not seem to offer a free additional driver? Pretty much unlike the rest of the major car rental corporations. A free additional driver by virtue of status is limited to rentals in the US.
Does anyone know of a way to add another driver for free for rentals in Europe? For instance by booking through an airline partner portal or through another affiliation?

KLflyer, did you find a solution? Is a spouse automatically allowed to drive, or does he need to pay as well? It always strikes me as tempting renters to compromise on safety, for long drives.