Snapshot - setting a multisite backup

Hi,
I run a multisite with documentation for my templates (that means adding one more site each time when new template is developed). I want to set a multisite backup in Snapshot which will make a backup for WHOLE multisite (twice i month), how I will achieve that? I just can't figure it out and at this point it looks like I can do it for one domain (that will mean do it one by one, each time when I add something I'll have to remember to add as well into snapshot = that's not what I want to do). Thanks in advance