How do you apply online for a job without posting your Social Security Number?

Every online job applications I have run into over the past six months is requiring a social security number be posted. It will not let you process without one. I have been advised that legally they should not be asking for this information until the applicate is accepted for interview or applicant agrees for a background check. So how would someone go about applying for the job online without posting their SS$?|||Try writing all zeros or leaving it blank.