I post a coin4.me short URL for some free coins in some local geocaches - or even just QR codes in public places around the neighborhood that point to the same short URL.
This URL typically redirects to a query string that contains information about the bitcoin address so that the page can display the amount stored in the wallet. But I can also include a merchant code just as easy. The idea is that when the hunter finds the QR code/URL, they will get a message that says "you can spend these 2 bitcoins, worth $10 at Joes Pizza just around the corner. If someone already retrieved this money, mention Bitcoins for a 10% discount".
I'll have an agreement with the merchant to exchange the Bitcoins for cash (if they want, and at a discounted rate so I can kinda recover some of the money I front for the campaign).
That's what I'm thinking anyway.
Bitcoin: Use it like Groupon, but without the excessive fees.