I wonder if you could attach multiple lines to a bar/triangle that's fixed under the balloon. This would eliminate the rope twisting/untwisting, but of course nothing stops the balloon itself from rotating.
to 90000'? that would be a tall order no pun intended. the bar would be heavy. one thing to keep in mind is that the gas will continue to expand, so that the size of the balloon visible in the GP's comment show it about 8' on the ground which is similar to my experience. by the time the balloon reaches burst altitude, it has increased in size to about 45'. this is part of the reason for needing such a long rope which allows for the swinging and torsion to this extent