Hi Andrew,
This isn’t currently possible; though, we are currently working on incremental backups, which should accomplish the same thing (e.g. a full backup every week, and then a daily backup of the changes since the last full backup)…
You can currently accomplish this another way, if you have shell access to your webserver – you can set up a cron job on the command-line that is configured with whatever schedule you please, and which uses a different cloud storage method; and that will get the same result – I can send more details on that if that’s a possibility.
Best wishes,
David