Right...and that's what I said in my earlier response: "...the text in that issue speaks of solving the problem in the other direction." Truly that issue should reflect a more general (either direction) approach for integrating the client-side stuff with the server-side stuff.
That said, it's not impossible to solve the problem with Spring Social as-is: There's no reason why you can't create a controller that is injected with the ConnectionRepository and uses it to save a connection...a connection that is created from the token given to it from the client-side. You can create the connection by calling createConnection() on the FacebookConnectionFactory, passing in an AccessGrant instance.
It's a lot more manual work on your part (which is why it'd be nice for Spring Social to directly support it), but it can be done.
Spring Social Project Lead