The problem with outputting to trim is that sometimes printers want the 4-sided bleed on every page. I wish that there WAS a workaround besides just not using facing pages. I usually design brochures/booklets as facing pages. Unfortunately, for a 100 page book, I had a stylesheet where the type was set up to be justified “away from spine”, so when I changed the layout to non-facing pages, I had to manually justify half of the headers.