The IRS issued Announcement 2011-21 which designated the Form 8955-SSA as the form to use for reporting separated participants with deferred vested benefits. The IRS has released a draft of Form 8955-SSA as well as posted FAQs on their website.
The Announcement indicates that the IRS has developed a voluntary electronic filing system for filing Form 8955-SSA which is ready to accept filings when the form becomes available for filing.
Form 8955-SSA has the same filing due date as the Form 5500; an extension can be obtained by filing Form 5558 which is being revised.