Wouldn't hook it to the depower line unless you are planning on unhooking as that would be more of a "suicide mode" set up and you wouldn't be able to fully flag the kite if needed. You could try and get hold of a newer naish bars swivel or similar and then a safety line could be run through the bar. The way it is now I can't see being able to run a line through the bar because that ring and red stopper ball would jam in the bar if the kite was released.
That swivel and yellow line is what I would do.