i was looking for the same thing, but not to force a user into liking something, but actually for their own protection.
here is where i come from: on a web site (maybe on multiple pages) there is an "I Like" button, implemented as described by facebook.
each time a user goes to that page, the browser will make a request to facebook, throught the iframe that contains the button, providing all the info that we are used to from a web server log file.
if the user has in the past logged in facebook and not cleared the cache. the request will also contain the cookie indentifying the facebook user.
so even more then analytics, facebook know all about the user activity on those pages.
so i wanted the user to only give this info when they decide to.
my solution was to have a button (as graphic only) on the page. when the user clicks it a new frame should open and only there the facebook code should be executed.
obviously on the new frame i could not put the normal "i like" code, since that would require a 2nd click for the user. at this point i would need the "programmatically clicking of the i like button".
it is not an opengraph solution, but it works: the frame just does a redirect to
http://www.facebook.com/share.php?u=URL