Don't worry, lack of z-order is bugging us internally as well, so it won't be long before we implement it in the software. It won't require an app update.
We recommend against using 'merged pages', these were implemented before subpages were available in the software. Subpages are far more efficient internally, and easier to work with. I'd need to check, but I think portrait and landscape objects are merged to the associated page when you create a page link.