I thought there was an official GOTM sticky, but I couldn't find it for some reason. If there is, feel free to move this post there!
I came upon another GOTM technique on one of the horse email lists I'm subscribed to. What you do, is lead the horse up to a low barrier (like a barrel on its side). Then, simply lure the horse's head (or use a target) over the barrel and down and as far out as it'll go. The horse will step up with his hind legs to compensate, and at that moment click. Continue luring his head out and clicking for hind leg movement (even putting a voice cue on it) until he won't move his hind legs any farther. (At that point, you can see how far he is physically capable of doing GOTM, if one leg is consistently taking less weight, etc.)
This worked AMAZINGLY well. As many of you know, Caspian and I have simply never been able to get GOTM. Before AND I tried to teach it with pressure (totally didn't work). In AND, I continued trying to teach it... and it still didn't work. He'd get stressed and would never understand and got very confused and thought I wanted hind leg jambette and just hated it. However, with this technique, the very first time, within just a few minutes his hind feet were probably within about 18 inches of his front feet. The second session (after my ride) went much faster and within almost no time at all his back feet were maybe a foot from the front!? And he stood like that, quite content. Magic!!