As an alternative to account owners having to send out invitations to all their drivers individually, perhaps promo codes could have the function to assign an invitation so that the account owner could give out the promo code and when applied it would automatically assign the user to the relevant account
Promotion codes probably aren't the best way to do this (if a promotion code was guessed or leaked to someone that shouldn't have access to the account, for example...) and as such we will not be pursuing this path.
We will, however look into other methods of "automatic invitations" potentially based on the account owner's e-mail domain.