I think I can clearly claim to be one of the first to post a design about the concept. I posted this picture in a thread back in Jan-Feb of 06
There was a guy selling 80% AR lowers back in 2003 or 2004 at the Costa Mesa gun show.
He was selling them with a shortened mag catch and two buttons that were sectioned in half.
The rear button still had threads and fit down into the reciever.
The front button got retained into the reciever with two setscrews, one from above and one from below.
He was demonstrating the release using a round of 223 ammo and had a whole page written up showing how it was legal to build such an AR as it would not be considered a detatchable mag per the wording of the law.
This was WELL before the 2005 gold rush to buy AR recievers.
I wish I could find that piece of paper because THAT guy really deserves the credit for bullet buttons as we know them now.