The bulk of ConnectController and ProviderSignInController's main functionality is already extracted into ConnectionSupport. So you could always write your own controller with its own mappings.
That said, there's still a lot of controller-specific code in both of those controllers. I suppose both of the controllers could be extracted into an annotation-less form of themselves with a new very thin annotated controller class delegating. Then you'd only need to create a custom annotated controller class to change the mapping. That's something worth considering.
I'd also want to consider what Spring 3.2 offers that might address this. I'll consider both options and see what I can come up with (probably in the 1.1.0.M3 timeframe, although I've not yet planned out the details of M2 or M3).
Spring Social Project Lead