I would imagine that this is possible, but you would have to go to trial and have the victim testify that you did not participate at all.  But rather it was the co-defendant that did everything and you were just someone in the wrong place at the wrong time.  If the victim will testify as such, then you have a good shot.  If just the co-defendant says that, you still have to deal witht he victime.  the jury will see that your buddy is being nice, but that doesnt take away from the fact that you were there and watched... if the victim will testify that you didnt do anything, then the state should cut you a break.  they could however try to charge you will something else as i do not know all the facts.