If it were my I'd get some thin elasticy type of cording and I'd put weights on the bottom. I'd tie each of the main branches down, start with lighter weights and get it to bend and then bend a little more each day with a little more weight so that she doesn't break. You could use metal washers on the cord because they have a hole in the center and every day you could add however many necessary to bend until you have it where you want it. but I'm a newbie and I don't know squat. All I know is I am bending and stretching the hell out of one of mine and it's awesome! Good luck to you.
you could also do a search for supercropping, mainline and training, there are a ton of threads on here about all of that.