So today I did a Thumb Grind to green triangle. Not sure if anyone else has figured out a way (I assume someone has) But I figured out a way to do it today, so ill explain.
Know Wrist whip? Make a motion like wrist whip so slack goes around your wrist. Catch the yoyo in a Thumb Grind. There will be that slack making a big loop around your wrist. From thumb grind drop the yoyo onto the bottom of the slack loop. Have your NTH index finger in the normal GT position. Drop the string off from your wrist, into a Green Triangle!
Enjoy! =D
cool now try doing it out of a GT