Steve, I didn't hear the start of the 648 broadcasts and only recently discovered this board, but from the lyrics you quote it sounds like the artist Graham Central Station, who did an a cappella track called 'We've Been Waiting'. This was a rendering of Frederick Knight's 1972 Stax single 'I've Been Lonely So Long'.
It's on YouTube, but I haven't posted a link in case of copyright issues, but you should be able to find it easily. Hope that helps!