I guess there are variations on everything, but when I've found myself in the enviable position of putting "two in the pink and one in the stink," it's been an index and middle finger inserted vaginally and a well-lubed thumb in her butt. I enjoy feeling my fingers and thumb rubbing against each other. The index and ring finger seems a little awkward. I do like your "Leather Cheerio" euphemism. Never heard that one before.