Honestly, I quit worrying about cracking the main trunk when I train. I used to spend four or five days bending the main trunk nice & slow, trying to slowly get that graceful 90 degree bend over a long 1/4 circle radius. But like it or not, I'd come back the morning after and the nice smooth radius had crimped over into something between a 45 and 90 degree bend. First few times, I was "Oh SHIT!!!" get out the gauze tape and the splints, fix her up, do the ganja shaman dance, pray to the weed gods.... but after a few times, seeing the plant never miss a beat, even dissecting a few crimps at the end of the grow, I realized all it was doing was the same as cracking or super-cropping. Now I bend them 45 degrees first day, get to 90 degress next day, and by morning three expect to see that crimped trunk.
But Man, oh Man, the increase in primary buds is phenomenal!!!