How should you tell a date that you don't want to see them again, without hurting their feelings?

You can't completely. But you can minimize it by being polite and firm and tell them you do not enjoy the pleasure of their company. The earlier you say this the less it will hurt.

Tell him that you think he's really great but next time he takes you out can you borrow his credit card so you can buy your dog the latest tiffany dog tag.