This may not be exactly in line with what you're asking, but here's a couple things I've been using extra scents for:
Scenting my stuffed animals/plushies. If there's a scent that fits thematically for an object, I'm happy to apply it! BPAL's Amsterdam didn't agree with me, but the grassy/floral scent was perfect for a plush sheep I have.
Giving a few sample vials away to friends to spark their interest in indie perfume houses
Scenting the paper used for scrapbooks or letters sent to friends!