My favourite oddball ingredient for a tomato based BBQ sauce is Lovage. It will add a peppery celery like taste with a hint of anise. Lovage can be difficult to find but is easy to grow in your garden. I always add some corn syrup or glucose to a tomato based BBQ sauce. It give the sauce that shiny glossy texture. But do not use glucose as the only sweetener, add others for flavour like molasses.