Can I send membership reminders "retroactively"
This answer assumes that this is a one-off requirement to deal with the "backlog" of reminders that has arisen because you haven't had the ability to send scheduled reminders before and that once the site is established you will be sending reminders at 2 months before the membership end date.  

You wouldn't do this with a scheduled reminder.  You would use Advanced Search or Find Membership to identify all those who "missed" the two-month-before reminder and send an email to them using CiviMail.