A quick search of Google Books suggests this figurative phrase is fairly recent.
New York Magazine (28 Jun 1982 - Page 15 - Vol. 15, No. 26) has an article on public speaking:
Maye adopts the Socratic method and teases out of us the idea that answering questions is a welcome way to clarify points and resell your audience. But how to prompt people into asking any?
"Have a transition question of your own in your back pocket," she clues us. "Raise your own hand and ask it."
