We went this weekend and my son got picked by yelling "pick me, pick me"

and jumping up and down. Your best bet is wait for the crowd to clear out from a previous show and stand up next to the rope and wait for the next show to start. I think it's about 30 to 40 minutes in between. Have you child jump and yell and hope for the best. At the end of the training they get a certificate and a Star Wars action figure. My son got a Clone Trooper.
We then waited in line for the store. It only took about 30 minutes and a Jedi cast member walked through the line handing out Star Wars action figures to the kids. Very cool

!
Once we got in the store we purchased a Darth Mickey.
We will be back next weekend!
May the force be with you all...
Tom