Client Portal Login - prepopulate with client's primary email address?

When creating a new login you are asked to enter an email address. 11 times out of 10 this would be the client for whom you are providing the login, there may be some exceptions but rare. Could this field be changed so that you can select an email linked to that client or enter an email. Every time I use this, I have to come out of it, back to the client to copy the email, then back to access.