1. The participant should register for the event with Username A and the personal email address.
  2. The participant should not use autofill.  He or she should register for the event again, but should use Username B and a business email address.
For registrations, one registration form completion equals one username and one registration record.  By registering with different email addresses, 2 different constituent/supporter records and ids will be created.  Do not merge the records, or the user will not be able to log in.