Yes, something not in the X-sheet but moveable. I don’t want to import an image not going to be in the animation so for me the x-sheet layer is out.
I’m going to go out on a limb and reference Artrage 6. They have something like that where you can pin reference images around your work area. I understand keeping the area uncluttered though. Even though I can use two monitors, I find it a strain to have to keep glancing between them, but that might just be me.