I'm pretty sure you can't teach turtles or tortoises tricks... As well, corn is a bad choice of "treat," or food at all. Tortoises have been known to play with balls (i.e. tennis balls), so maybe he'd be interested in that, but I highly doubt you'd be able to teach the turtle a trick. Remember, reptiles aren't dogs... They don't have the intelligence, motivation, or desire to please that make dogs so easy to train. Very different animals...
I highly recommend reading through this Box turtle care website:
http://boxturtlesite.info/ and posting on this forum:
http://tortoiseforum.org... You can ask about your "training" theory on the forum to see if anyone has any input for you.