jim8flog
Journeyman Pro
I was on about this only yesterday when Baghead played a provisional, we let through a two ball whilst looking for his first ball. One of the two ball walks past and looks at bag heads ball and says that's mine. It was (previously). Baghead said he would give it him back in the clubhouse but he lost it. 
Outta interest. Could you actually give it him back during a hole or would you have to wait til the end of the hole.
You would have to wait until you finished playing the hole completely unless you damaged the ball with another shot or did something like hit it out of bounds.