One time password to email - can we make external email to be default?

We use ADSelfService Plus for users to unlock them selves. We use Email One-Time password as multi-factor authentication method. A lot of times, we get our users telling us that they did not receive One Time Password email, and it turns out that their email in active directory is the default email selected for One Time Password. I think this would not make sense to a lot of companies because most of the time, if the user is locked out from ActiveDirectory, they cannot check the email associated with their active directory user account which is locked out. So, it would be better to make the external email address selected by default or send one-time password to both Internal and External email addresses.
Or... I may have missed something. Is there a way to configure ADSelfService send One Time password to both internal and external email addresses of the user?