After fiddling with StreetCred (a gem to handle Facebook credit integration) for a few weeks, I have a basic version available, as well as a working example at https://github.com/ragingsquirrel3/feed_the_giraffe, with some disclaimers.

Right now, the callback response is static.  The next feature I will need to add is the ability to specify product information.  For now, however, the example will stand as a proof of concept.