So just straight up ask the person "Have you ever thought about us hooking up?". If they don't want it, they'll just decline, and you can both get over it. Or they'll think you're a creep, and you won't be friends anymore, which is probably for the best seeing as you were harboring secret desires for this person.
Either way, being up-front and honest will have a better result than letting Facebook connect you because you were too scared to broach the subject.