We have just added the ability to auto-post your recurring transactions. This will give you the ability to add recurring transactions to the site before they are scheduled to.
To use the Post Now feature, go to the Reminders/Recurring transactions page and you will see a "Post Now" link next to each reminder with an associated transaction. Click on that link and it will auto-post it to your register dated with whatever the reminder date is.
The reminder will still run on the scheduled day, but the transaction will not be posted since you already clicked the link.