I think the problem here is to assume that "skeptics" are an homogeneous group that will club together. The skeptical community (whatever that is) tend to be free thinkers with highly individualistic views, with the capacity to debate their point of view very powerfully. I suspect "clubbing together" will almost be an anathema to many of them.
Sorry not my thing but isn't a alpha course "a practical introduction to the Christian faith"? That's what Wikipedia says anyway and when has that ever been wrong?
You may well be able to bring together the faithful as faith by definition is something you believe in without thinking about or believe in, knowing it can't be true (the former being ignorance and the latter being denial). That's the diametric opposite of skepticism, isn't it?