Separate vertical layout of viewer pane and metadata pane?

I must be missing something obvious because I can't figure out how to put the viewer pane and metadata pane into separate vertical sections side by side instead stacked on top of each other. The metadata pane seems to warrant more vertical real estate when there's long lists of metadata, and a more "portrait" style view of the viewer pane would be useful for skimming through PDFs and other page shaped documents. I'm trying to make a layout with three vertical sections: single folder display, metadata, viewer. (I don't use a dual display or a folder tree because I like to just have a bunch of tabs open in a single display and zip around it with ctrl+tab.)

You can't, at least currently. If both the viewer and metadata panels are vertical then they'll always stack on top of each other.