You need to know Wrist Whip for this. First, do a Wrist Whip, but quickly stick you nonthrowhand index finger in the loop. Land the yoyo on the string closest to you or a.k.a. the bottom string. You’re in a GT. 
The old spencer also found this out ;D
http://yoyoexpert.com/forums/index.php/topic,2718.0.html
Gerard also made a tut on this.
You know, a lot of people think I’m him. I’M NOT!!! I looked at his trick, mine was different. He did an underpass and dropped it in. I stopped the whip and landed it on the bottom string. I try to make up tricks and you guys think I’m him! I’M NOT. I just want to know if you guys like my tricks. 
I never even said you are him, i just said he did something similar. I don’t really understand the trick though. Can you make a video? I’m not saying you are the other guy. I really didn’t.
Oh. Sorry. :-X I don’t have a camera… :-\