I had a job last year that I initially thought was to retrieve a fixed wing, turns out it was a gyrocopter, so probably a fair bit easier to move than a plane. I did call a local legend pilot who had done it many times under a Lama, and he gave similar advise to the posts above: Strap some timber or anything to the top of the wing to spoil the airflow and therefore lift. Use a long line (minimum 100 ft). Sling the aircraft in a nose down attitude, and as mentioned above add some sort of drag /drogue chute to keep everything moving straight. I think that was pretty much it.
Small gyrocopters as it turns out sling surprisingly well