well, i had "invented" this method by myself. Its all about the crosshatch, which I had firstly drawn (I had a .dwg file of that crosshatch, but I had somehow lost it). Than you just scarify certain dashes of the crosshatch from the top, certain dashes from the bottom -according to the side from which you want to bend it. And then you are just carefully bending according to scarified lines.
.)