Referral Candidates User Name

Summary

Is there a way to make the user name for a referral candidate their email address rather than the candidate reference number?

Content

When an employee submits a referral, the user name is their candidate reference number.  The email does provide a link to the career section and gives them the user name, but we are using Jibe as our career site administrator and the log in field there says Email Address, so if referrals go there they are trying to enter the email, but it should be their candidate reference #.   

Does anyone know if there is a way to automatically assign their email address as their user name rather than the candidate reference number?