I think the question he had was not so much what to use to feed the +5v in with, but where to place the black wire from the wall wart. I understand where his confusion comes in as this is really quite counter-intuitive to non-electronics folk.
I understand how this works with some types of breakout board, but I do not know enough of electronics to feel safe suggesting a catch-all solution for different types of interface - I am unfamiliar with the fundamental differences in electrical behavior between directly interfacing with the port vs. outputs from another opto stage, and don't want to suggest something incorrect.

Perhaps one of you guys could indulge us with a bit of an education on what the signal is actually doing here to help visualize, or perhaps just a recommended way of doing it most simply? I'd be interested in this, too.