Non-standard login form - Options?

How can I handle non-standard website logins like the 3 part 'user name' field illustrated below?

 

Sprint Family Locator Login page 

 

Are there any 'custom' form filling  to handle this special situation? If not, is the only alternative to uncheck the 'auto-fill when I visit this page' option under 'Edit Logins'?

 

Thanks,