there is no way to do it out of the box, you could either:
1. get a developer to customize the system to add the Incoming Document Files factbox that exists in the general journal to the recurring general journal page
2. after the recurring general journal is posted, if you navigate to the general ledger entries created, you can add an attachment to the posted entries from there. Its a bit of an workaround but it will achieve what you are looking for
