uhh - nohelp - I'm not certain that syncing with an empty folder actually removes your files.
Go into the portal, select my account and then view files - in the middle of the window are a date & time pulldown - it that works the way I think it does, you can select an earlier "view" of your files and restore from there.
It starts to get interesting here - how is my storage utilization being measured?
For the sake of discussion - let's say I've been backing up 40GB of data on a daily basis and then I delete 20GB of it and add another 20GB, I wait one day so that is backed up and then delete 30GB and add 30GB more and then a day later I wipe the data off of my DNS-323
Theoretically I can now choose to restore from the original 40GB of data - from the 20GB of new data that was backed up two days ago, or the 30GB of new data that was backed up yesterday - for a grand total of 90GB.
It's not that I'm looking for a way around the restriction, but, I'd hate to know that my 40GB of data with a month of shadows is being billed as 1200GB when I thought it was 40.