How can I automatically confirm a secondary email address?

This is not a direct answer to your question, but: In the case of mass-renaming of email-addresses, you could do it via rails console:

o = "@old_company.com" 
n = "@new_company.com"
UserEmail.where("email LIKE ?","%#{o}").each do |ue| 
  ue.email.sub! o,n 
  ue.save! 
end

If you favor adding a secondary email address:

o = "@old_company.com" 
n = "@new_company.com"

UserEmail.where("email LIKE ?","%#{o}").each do |ue|
   sm = UserEmail.new
   sm.user_id = ue.id
   sm.email = ue.email.sub! o,n
   sm.save!
end