You can copy and paste button on different layout. You can have buttons to perform a script and you could have the same script connected to buttons on different layouts. When you edit the script then the changes would apply across all layouts because it is based on the same script.
I guess I didn't explain the problem clearly.
What you describe is what I do now. What I would like to do is add a new button to the group one place and have it appear in all the layouts I use that specific array of buttons.
There is no such new feature in FileMaker 12. It would be nice if there were, but there isn't.