As it is now, Spring Social's connection flow support is based on Spring MVC web controllers. So, that (probably) won't work in Liferay (I say "probably" because it has been awhile since I've looked at LifeRay, so I'm not sure of the details here).
But Spring Social's controllers are just a high-level controller-based abstraction on top of the rest of Spring Social's connection framework. If someone who knows how to write Liferay portlets were to dig into the code for ConnectController, they'd probably be able to figure out how to write a Liferay portlet that does the same job as ConnectController.
I don't know how to do that and it is a somewhat specific use-case, so I don't plan on implementing it (unless there's a large enough community demand for it). But if you or someone else is willing to do it, then I'll be happy to assist as much as I can. And, I'd be especially happy to help you get it working if you were to contribute a ConnectPortlet (or some such thing) back to the Spring Social community. Let me know how I can help out.
Spring Social Project Lead