Through the glorious wonder of science, I have managed to keep the Thunderspark powered precisely for this purpose.
All you need to do is get to the Temple of Storms and absorb Hati's essence into it. Just... kind of point it in his general direction.
Oh, and do keep in mind that this is only one part of Hati. You may run into a few... technical difficulties before he's subdued enough for the absorption protocol.