Hmmmm...just quickly reading over msdn articles on switching it seems you can only switch a partition with an empty one. So then I would see it as a three partition cycle.

1. Staging -> Holding

2. Main -> Staging

3. Holding -> Main

4. Delete Staging

or perhaps simply

1. Main -> Holding

2. Staging -> Main

3. Delete Holding

Thanks folks, I'll have to do some more reading and testing but it sounds promising.