This feature would be an extension to an fb connect button, but once they do that if we could then send them "notifications" to their fb page it could really simplify the sharing cycle.
You can make the notification go straight to the fb sharer, or to the upviral page that shows all the share options and how far along they are to unlocking the milestone prize. If we could add some text to it like: "You're so close! you have 3/5 sign ups to get "x" prize!"
I think seeing it right there while they are in the social network you want them to share it in, could go a long way. It keeps them in the "social state of mind" they are currently in, and encourages them to do something people do while there.
It also gives them something to post, alot of times people want to post, but dont know what to post.
The FB Notification feature is very attractive to spammers. We've had that earlier - and people simply abuse it (which leads to an angry FB - which is something we don't want).
For that reason this isn't something we can't implement - sorry..