Actually, the Packers signed PJ Pope an undrafted rookie, off of Chicago's practice squad. My guess is that the move was made as much to find out about the Bears themselves as well as their approach to their opponents as it was to add a decent running back to the roster. The Pope only averaged 3.8 per rush in the preseason.
Coach: "Good to have you with us PJ. Now sit down and tell us all you can about the Bears."Pope: "Uh... well... I wuz just on duh practice squad, but... mmmm... lemme see... Brian Urlacher's really good..."
Coach: "Wait, hold on, my pen's out of ink. I need to write this stuff down... here's another pen. 'Brian -- Urlacher's -- really -- good.' Got it. OK, what else..."