Well, to port JJ2 to Facebook, you'd need to port it to HTML5 or Java(Yes, you could port it to Flash, but Flash is slow and is probably going to become obsolite because of HTML5), and that would be quite a tough job.
Besides, first we'd need either the JJ2 Sourcecode, or the Plus Developers to reveal some of their secrets to someone willing to port JJ2 to HTML5/Java, and even if the latter happened, the afformentioned person would probably have to do a fair amount of guesswork to get the game to work completely.