Allow user to choose role immediately after registration
I solved this by using the Rules module and 2 basic pages. Not a very scalable solution, but works in this limited application.


User registers using Facebook Connect or the core Drupal registration process.
The new user with the "basic" role is redirected (via Rules) to a "select your role" page with links to a "Welcome new driver" page and a "Welcome new owner" page.
Upon viewing the node, "Welcome new driver/owner", with the role "basic" a rule is triggered which sets the desired new role, removes the "basic" role and triggers role-specific welcome email.