It's not really the metaphor, though, it's the actual plot. The Source is a mystical plug that keeps evil contained. It has a protector that, we can guess, has the ability to push people. That's not in Joss's original idea where it was the Master getting stuck in the Hellmouth.

You could say even then, though, that Joss had all this plotted before Lost was over, but there are quite a few similarities and when you add in all the other shout-outs/homages, it's a little sigh-worthy.