Multiple Frame Layers
So I guess it was pretty obvious that putting more than one _frame layer on a page should just work. It's a common design paradigm. People would use it. And you let me know.
So yesterday I made a minor modification to how the _relative and _frame Layer Naming Conventions work together. Now you can put multiple _relative_frame layers (use both _relative and _frame in the same layer name) to get exactly what you want. Make sure you put them inside some container layer - it can even be _empty. The _relative_frame layers (and any content, text or other layers inside them) will stack up nicely in your container.
Here is an example of some _relative_frame layers in action. Click on the link to put random text inside the _relative_frame layers to see them work:
Here is the PSD file used to make that page: