I'm wondering if the bars on different size wings are different length. Can anybody who has seen the different sizes in the wild confirm that?
I would expect they do in order to match the steering input to the size of the wing, and to allow the wing to be brought close to stalling using the bar.
If that is the case then pointing the bar at the wing, will create the maximum difference in length between the front and rear lines. That will either stall the wing, or bring it close to the stall point so you can tweak the back lines and create a stall. Once it's stalled it should be easier to pull in the lines and gather the canopy.
You want to time the stall so that you're ready to grab the wing. If you over stall the wing will invert and buck. If you partially release the stall the wing will re-inflate and surge.
I have seen on one of the videos the rider points the bar at the wing then slides his free hand up the bar from the trailing edge and along the lines. In others they just grab the canopy and bunch it.
A brief surge downwind will ease the tension on the lines making it easier to pull in. Loading the board and wing upwind will increase the tension on the front lines and make the canopy much more rigid.
Here's a couple of videos where people run their hands up the back lines.