MidAtlanticFoil said..After my first (overpowered) session with the 4.3M, I've been brainstorming around a good reverse harness hook solution for the S3 and the D handle. Hooking in at the shaft side of the handle means full on power, while hooking in to the front of the handle means full on depower.
I've yet to try this, but I used a 12" or so piece of dyneema and a clove hitch and a random hitch knot to make this small line that bridges the gap of the handle. I'm hoping that this makes the perfect catchers mitt for the hook to reside.
I almost always ride one handed, unless I'm really focusing on most efficient upwind angle.
Only downside I see is though can't fully put your hand inside the handle. That's a good thing in my opinion. In Jeremy's vid above, he showed one technique of putting your hand up inside the handle, but that could be pretty dangerous in a wipeout and could easily lead to a broken hand due to the lever moment of something (board/knee) hitting the end of the bar.

Why not use the dyneema and tie a mini version of Greg's harness line? Instead of the long loop, just make that leg much shorter. From flying my 5.3, that spot just in front of your thumb seems to be the center of lift. Putting your reverse J attachment loop there would be the same as having the reverse J hook right behind the A line cluster on a bar.